# Is this number a prime?

Believe it or not, we do not yet have a code golf challenge for a simple primality test. While it may not be the most interesting challenge, particularly for "usual" languages, it can be nontrivial in many languages.

Rosetta code features lists by language of idiomatic approaches to primality testing, one using the Miller-Rabin test specifically and another using trial division. However, "most idiomatic" often does not coincide with "shortest." In an effort to make Programming Puzzles and Code Golf the go-to site for code golf, this challenge seeks to compile a catalog of the shortest approach in every language, similar to "Hello, World!" and Golf you a quine for great good!.

Furthermore, the capability of implementing a primality test is part of our definition of programming language, so this challenge will also serve as a directory of proven programming languages.

Write a full program that, given a strictly positive integer n as input, determines whether n is prime and prints a truthy or falsy value accordingly.

For the purpose of this challenge, an integer is prime if it has exactly two strictly positive divisors. Note that this excludes 1, who is its only strictly positive divisor.

Your algorithm must be deterministic (i.e., produce the correct output with probability 1) and should, in theory, work for arbitrarily large integers. In practice, you may assume that the input can be stored in your data type, as long as the program works for integers from 1 to 255.

### Input

• If your language is able to read from STDIN, accept command-line arguments or any other alternative form of user input, you can read the integer as its decimal representation, unary representation (using a character of your choice), byte array (big or little endian) or single byte (if this is your languages largest data type).

• If (and only if) your language is unable to accept any kind of user input, you may hardcode the input in your program.

In this case, the hardcoded integer must be easily exchangeable. In particular, it may appear only in a single place in the entire program.

For scoring purposes, submit the program that corresponds to the input 1.

### Output

Output has to be written to STDOUT or closest alternative.

If possible, output should consist solely of a truthy or falsy value (or a string representation thereof), optionally followed by a single newline.

The only exception to this rule is constant output of your language's interpreter that cannot be suppressed, such as a greeting, ANSI color codes or indentation.

• This is not about finding the language with the shortest approach for prime testing, this is about finding the shortest approach in every language. Therefore, no answer will be marked as accepted.

• Submissions in most languages will be scored in bytes in an appropriate preexisting encoding, usually (but not necessarily) UTF-8.

The language Piet, for example, will be scored in codels, which is the natural choice for this language.

Some languages, like Folders, are a bit tricky to score. If in doubt, please ask on Meta.

• Unlike our usual rules, feel free to use a language (or language version) even if it's newer than this challenge. If anyone wants to abuse this by creating a language where the empty program performs a primality test, then congrats for paving the way for a very boring answer.

Note that there must be an interpreter so the submission can be tested. It is allowed (and even encouraged) to write this interpreter yourself for a previously unimplemented language.

• If your language of choice is a trivial variant of another (potentially more popular) language which already has an answer (think BASIC or SQL dialects, Unix shells or trivial Brainfuck derivatives like Headsecks or Unary), consider adding a note to the existing answer that the same or a very similar solution is also the shortest in the other language.

• Built-in functions for testing primality are allowed. This challenge is meant to catalog the shortest possible solution in each language, so if it's shorter to use a built-in in your language, go for it.

• Unless they have been overruled earlier, all standard rules apply, including the http://meta.codegolf.stackexchange.com/q/1061.

As a side note, please don't downvote boring (but valid) answers in languages where there is not much to golf; these are still useful to this question as it tries to compile a catalog as complete as possible. However, do primarily upvote answers in languages where the author actually had to put effort into golfing the code.

### Catalog

The Stack Snippet at the bottom of this post generates the catalog from the answers a) as a list of shortest solution per language and b) as an overall leaderboard.

## Language Name, N bytes


where N is the size of your submission. If you improve your score, you can keep old scores in the headline, by striking them through. For instance:

## Ruby, <s>104</s> <s>101</s> 96 bytes


If there you want to include multiple numbers in your header (e.g. because your score is the sum of two files or you want to list interpreter flag penalties separately), make sure that the actual score is the last number in the header:

## Perl, 43 + 2 (-p flag) = 45 bytes


You can also make the language name a link which will then show up in the snippet:

## [><>](http://esolangs.org/wiki/Fish), 121 bytes


<style>body { text-align: left !important} #answer-list { padding: 10px; width: 290px; float: left; } #language-list { padding: 10px; width: 290px; float: left; } table thead { font-weight: bold; } table td { padding: 5px; }</style><script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/codegolf/all.css?v=83c949450c8b"> <div id="language-list"> <h2>Shortest Solution by Language</h2> <table class="language-list"> <thead> <tr><td>Language</td><td>User</td><td>Score</td></tr> </thead> <tbody id="languages"> </tbody> </table> </div> <div id="answer-list"> <h2>Leaderboard</h2> <table class="answer-list"> <thead> <tr><td></td><td>Author</td><td>Language</td><td>Size</td></tr> </thead> <tbody id="answers"> </tbody> </table> </div> <table style="display: none"> <tbody id="answer-template"> <tr><td>{{PLACE}}</td><td>{{NAME}}</td><td>{{LANGUAGE}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr> </tbody> </table> <table style="display: none"> <tbody id="language-template"> <tr><td>{{LANGUAGE}}</td><td>{{NAME}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr> </tbody> </table><script>var QUESTION_ID = 57617; var ANSWER_FILTER = "!t)IWYnsLAZle2tQ3KqrVveCRJfxcRLe"; var COMMENT_FILTER = "!)Q2B_A2kjfAiU78X(md6BoYk"; var OVERRIDE_USER = 12012; var answers = [], answers_hash, answer_ids, answer_page = 1, more_answers = true, comment_page; function answersUrl(index) { return "https://api.stackexchange.com/2.2/questions/" + QUESTION_ID + "/answers?page=" + index + "&pagesize=100&order=desc&sort=creation&site=codegolf&filter=" + ANSWER_FILTER; } function commentUrl(index, answers) { return "https://api.stackexchange.com/2.2/answers/" + answers.join(';') + "/comments?page=" + index + "&pagesize=100&order=desc&sort=creation&site=codegolf&filter=" + COMMENT_FILTER; } function getAnswers() { jQuery.ajax({ url: answersUrl(answer_page++), method: "get", dataType: "jsonp", crossDomain: true, success: function (data) { answers.push.apply(answers, data.items); answers_hash = []; answer_ids = []; data.items.forEach(function(a) { a.comments = []; var id = +a.share_link.match(/\d+/); answer_ids.push(id); answers_hash[id] = a; }); if (!data.has_more) more_answers = false; comment_page = 1; getComments(); } }); } function getComments() { jQuery.ajax({ url: commentUrl(comment_page++, answer_ids), method: "get", dataType: "jsonp", crossDomain: true, success: function (data) { data.items.forEach(function(c) { if (c.owner.user_id === OVERRIDE_USER) answers_hash[c.post_id].comments.push(c); }); if (data.has_more) getComments(); else if (more_answers) getAnswers(); else process(); } }); } getAnswers(); var SCORE_REG = /<h\d>\s*([^\n,<]*(?:<(?:[^\n>]*>[^\n<]*<\/[^\n>]*>)[^\n,<]*)*),.*?(\d+)(?=[^\n\d<>]*(?:<(?:s>[^\n<>]*<\/s>|[^\n<>]+>)[^\n\d<>]*)*<\/h\d>)/; var OVERRIDE_REG = /^Override\s*header:\s*/i; function getAuthorName(a) { return a.owner.display_name; } function process() { var valid = []; answers.forEach(function(a) { var body = a.body; a.comments.forEach(function(c) { if(OVERRIDE_REG.test(c.body)) body = '<h1>' + c.body.replace(OVERRIDE_REG, '') + '</h1>'; }); var match = body.match(SCORE_REG); if (match) valid.push({ user: getAuthorName(a), size: +match[2], language: match[1], link: a.share_link, }); else console.log(body); }); valid.sort(function (a, b) { var aB = a.size, bB = b.size; return aB - bB }); var languages = {}; var place = 1; var lastSize = null; var lastPlace = 1; valid.forEach(function (a) { if (a.size != lastSize) lastPlace = place; lastSize = a.size; ++place; var answer = jQuery("#answer-template").html(); answer = answer.replace("{{PLACE}}", lastPlace + ".") .replace("{{NAME}}", a.user) .replace("{{LANGUAGE}}", a.language) .replace("{{SIZE}}", a.size) .replace("{{LINK}}", a.link); answer = jQuery(answer); jQuery("#answers").append(answer); var lang = a.language; lang = jQuery('<a>'+lang+'</a>').text(); languages[lang] = languages[lang] || {lang: a.language, lang_raw: lang.toLowerCase(), user: a.user, size: a.size, link: a.link}; }); var langs = []; for (var lang in languages) if (languages.hasOwnProperty(lang)) langs.push(languages[lang]); langs.sort(function (a, b) { if (a.lang_raw > b.lang_raw) return 1; if (a.lang_raw < b.lang_raw) return -1; return 0; }); for (var i = 0; i < langs.length; ++i) { var language = jQuery("#language-template").html(); var lang = langs[i]; language = language.replace("{{LANGUAGE}}", lang.lang) .replace("{{NAME}}", lang.user) .replace("{{SIZE}}", lang.size) .replace("{{LINK}}", lang.link); language = jQuery(language); jQuery("#languages").append(language); } }</script>

• Is there a reason for the full program requirement, rather than allowing the full range of default input types? E.g. answering with a function that takes its input as an argument, is currently disallowed? codegolf.meta.stackexchange.com/questions/2447/… – Lyndon White Dec 12 '17 at 6:21
• @LyndonWhite This was intended as a catalog (like “Hello, World!”) of primality tests, so a unified submission format seemed preferable. It's one of two decisions about this challenge that I regret, the other being only allowing deterministic primality tests. – Dennis Dec 12 '17 at 12:51
• Could a case be made for locking this challenge and posting a new, less restrictive one? – Shaggy Jun 25 '18 at 12:59
• @Shaggy Seems like a question for meta. – Dennis Jun 25 '18 at 13:44
• Yeah, that's what I was thinking. I'll let you do the honours, seeing as it's your challenge. – Shaggy Jun 25 '18 at 13:45

C#, 116 bytes

Non fancy full program entry (cherry-picking some stuff from java):

class P{static void Main(string[] a){int i=2,n=int.Parse(a[0]);for(;i<n;)n=n%i++<1?0:n;System.Console.Write(n>1);}}


# C++ (gcc), 85 bytes

#include<iostream>
int main(){int n,d=1;for(std::cin>>n;n%++d%n;);std::cout<<(n==d);}


Try it online!

• -2 bytes thanks to @ceilingcat

# Ungolfed

#include <iostream>
int main() {
int n,d=1;
for (std::cin >> n; n % ++d      // Trial division. If n dividible by d, end.
% n        /* No effect when n > 1.
But required to make sure the loop ever ends if n == 1
*/
);
) { /* Empty loop body */ }  /* d is now the lowest number greater than 1 which
divides n (or 2 if n == 1)
*/
std::cout << (n==d);             // If that number is n, n must be prime.

}


Port of my Ink answer. Competitive in multiple other languages. I wasn't going to post this, but I couldn't find a C++ compiler that would compile the existing C++ answer.

• @ceilingcat well spotted, thanks – Sara J Jun 3 '19 at 18:34

# K (oK), 14 19 bytes

Solution:

2=+/d=_d:x%!x:. 0:


Try it online!

Example:

root@c957fa0dccbd:/ok# echo 1 | node repl.js examples/prime.k
0
root@c957fa0dccbd:/ok# echo 2 | node repl.js examples/prime.k
1
root@c957fa0dccbd:/ok# echo 5 | node repl.js examples/prime.k
1
root@c957fa0dccbd:/ok# echo 97 | node repl.js examples/prime.k
1


Explanation:

Calculate number of factors for input, if equal to 2, then it's prime.

2=+/d=_d:x%!x:. 0: / the solution
0: / read from stdin
.     / value (ie convert "123" > 123)
x:      / store input as x
!        / range 0..x
x%         / x divided by ...
d:           / store as d
_             / floor
d=              / d equal to ...
+/                / sum
2=                  / 2 equals?


# Rust, 124 bytes

fn main(){let s=&mut"".into();std::io::stdin().read_line(s);let n=s.parse().unwrap();print!("{}",n>1&&(2..n).all(|x|n%x>0))}


Try it online!

How complicated it has to be to read an integer from stdin...

# Ink, 68 51 bytes

-(l)
+(n)[+]
->l
*(r)[{n}]
{n%(r+1)%n:->r|{n==(r+1)}}


Ink was made for writing interactive fiction. It was never meant to be a general-purpose programming language. So it only has one way to recieve input.
Choice prompts.
So the way it works is, if option 2 is labelled with the number you want to check, you pick option 2. Otherwise you pick option 1 to increment option 2's label. So, if you want to check if 15 is prime, you'd input

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2


TIO doesn't handle this, unfortunately.

-17 bytes by using read counts of named options instead of creating variables. This brings the overhead of taking input this way down to something like 24 characters (or even 18 if we don't care about minimising the text from the prompts), compared to the 10 for defining a parametrised stitch and returning from it.

Since full programs can use global variables and read counts, but stitches that have to be reusable can't, using full programs might actually pay off in places where I thought it wouldn't. Neat.

# T-SQL, 116 bytes

WITH t AS(SELECT 2n UNION ALL SELECT n+1FROM t WHERE n<5e4)
SELECT*FROM z,t WHERE p%n=0AND n<p OPTION(MAXRECURSION 0)


There is an Oracle SQL answer here, but couldn't find a Microsoft T-SQL version for this classic question.

Notes:

• Line break is for readability only.
• Returns no rows if prime, returns 1 or more rows otherwise. This is allowed per this output rule.
• Input is taken via pre-existing table $$\z\$$ with INT field $$\p\$$, per this input rule.
• Handles values of $$\p\$$ up to the max value of the INT type, $$\2^{31}-1\$$

Explanation:

Generates an in-memory number table $$\t\$$ from 2 to 50k (which exceeds the square root of the max int), then joins to the input table $$\z\$$ and uses the modulo operator % to test for divisibility. Any values that divide evenly are returned, so an empty result means the input is prime.

OPTION(MAXRECURSION 0) is needed to recursively generate a table with more than 100 rows, unless you've altered this configuration setting on your SQL server.

Optimized for bytes, not speed; checks more values than is strictly necessary.

# Wren, 48 43 bytes

I feel surprised that I think better when using W instead of Wren. Also, the 1-primalty problem is fixed.

Fn.new{|i|(1..i).where{|x|i%x==0}.count==2}


Try it online!

• Fails for 1, just like your previous answer. – Jo King Dec 21 '19 at 22:23

# tinylisp, 23 bytes

There's a library function.

(load library
(prime? 1


(Since tinylisp is incapable of taking user input, "For scoring purposes, submit the program that corresponds to the input 1.")

Try it online!

Here's a 112-byte solution using only the base language, no library functions:

(d D(q((F A N)(i(l A N)(D F(a F A)N)(e N A
(d _(q((F N)(i(D F 0 N)(e F N)(_(a 1 F)N
((q((N)(i(e N 1)0(_ 2 N))))1


The first line defines a function D that takes a factor F, an accumulator A (initially 0), and a number N; it returns 1 if N is divisible by F, 0 otherwise.

The second line defines a function _ that takes a minimum factor F and a number N; it returns 1 if N is coprime to all numbers from F to N-1, 0 otherwise.

The third line constructs an anonymous function that takes a number N; it returns 0 if N is 1, and otherwise calls _ with number N and minimum factor 2. As above, the scored code calls the anonymous function with an argument of 1.

# Symbolic Raku, 17 bytes

$_=?($_%%[^] ^$_)  Try it online! Suprisingly, this is shorter than the my previous Raku answer, though one byte longer than using the built-in ### Explanation: $_=                # Set the output to
?(           )  # The boolean of
$_ # If the input is %% # Divisible by [^] # Only one of ^$_   # The range from 0 to input-1


## W d, 5 bytes

(Possibly the only <=5-byter that does not use a prime or number factorization built-in?) (The two spaces here represent a tab)

àTéBΦ


repr'd:'‡T\tB⑸'

Unpacked:

m!Wk2=


## Explanation

This is really difficult to read, so an explanation will be nice.

    W    % (implicit) Foreach the inclusive range from 1 to the input:
bam      % The "bam" magic! Just kidding. Evaluates b % a
% Since b is out-of-bounds, this takes the upper-level input
% as the operand.
!     % Remove those that aren't valid multiples.
k   % Is the length of the array ...
2= % ... equal to 2?
% i.e. primes have exactly 2 factors: 1 and itself

• Crax! That sounds like a good golfing language name. – lyxal Jan 1 '20 at 6:16
• I'm more saying that the source code looks like it says CRAX – lyxal Jan 1 '20 at 6:19
• Looks like there is a bug in the interpreter and I had to change the compression... – user85052 Jan 20 '20 at 0:14

# Keg, 43366 4 bytes (SBCS)

@MPƒ


-2 bytes using a BFL function

:;¡²$%  Try it online! -30 bytes thanks to @JoKing No TIO as it needs to be updated due to a bug found with the ² operator. Transpiles to: from KegLib import * from Stackd import Stack stack = Stack() printed = False duplicate(stack) decrement(stack) factorial(stack) square(stack) swap(stack) maths(stack, '%') if not printed: printing = "" for item in stack: if type(item) is Stack: printing += str(item) elif type(item) is str: printing += custom_format(item) elif type(item) == Coherse.char: printing += item.v elif item < 10 or item > 256: printing += str(item) else: printing += chr(item) print(printing, end="")  ### 36 bytes (SBCS)  ¿®n21®t{:©n≠©t0≠*|:©n$%[1|0]®t1+}©t.


Try it online!

-7 bytes by not using a variable to keep track of the count.

Explained

¿®n21®t{:©n≠©t0≠*|:©n$%[1|0]®t1+}©t. ¿®n #Take the number to check and store it in variable n 2 #This will act as the divisor counter 1®t #This will act as the return value, indicating the primality {:©n≠©t0≠*| #While the counter isn't equal to n and there isn't a divisor yet :©n$%             #Take the counter and number, then swap for modulus
[1|0]®t      #Depending upon the result set t to 1 if it doesn't divide otherwise 0
1+}   #Increment the counter


### 43 bytes (SBCS)

¿®n2®c1®t{©c©n≠©t0≠*|©n©c%[1|0]®t©n1+®c}©t.


It's a real ugly mess, but it works. I'll explain it all later. Also, doesn't work on TIO due to a bug that I found. It should work soon however.

Use the latest github interpreter

# cQuents, 3 bytes

?pZ


Try it online!

## Explanation

Usually, I'd put the commands here, but I feel like that wouldn't be enough.

? outputs if the input is in the sequence. Item 1: Z returns 0, as Z returns the previous item, and Item 0 is always 0. p finds the next prime number (2). Item 2: Z returns 2. p finds the next prime number, which I thought would be 2, but no, it returns 3.

# Haskell + Parsec, 181 bytes, no math

import Text.Parsec
a=anyChar
g s=a>>= \c->try(many1$string$c:s)*>eof<|>g(c:s)
main=readLn>>= \x->print$0<case parse(try(a*>eof)<|>(pure<$>a>>=g))""$replicate x '0'of{Left _->1;_->0}  Try it online! ### Ungolfed and explanation: import Data.Either (isLeft) import Text.Parsec (eof, (<|>), try, anyChar, many1, string, parse) import Text.Parsec.String (Parser) -- Successfully parses any string of nonprime length, and fails on all others. -- Exactly one character is not prime. If more than one character exists, we recurse with go. notPrime :: Parser () notPrime = try (anyChar *> eof) <|> (pure <$> anyChar >>= go)
-- go cs reads a character c and determines whether the remaining input is c:cs repeated.
-- If so, the parse succeeds. If not, we call go (c:cs) to read another character and test again.
where go :: String -> Parser ()
go cs = do
c <- anyChar
try (many1 $string$ c:cs) *> eof <|> go (c:cs)

-- Checks whether the parser notPrime fails on a uniform string of the specified length
isPrime :: Int -> Bool
isPrime n = isLeft $parse notPrime "" (replicate n '\0')  Try it online! # qalc/Qalculate, 8 bytes If reading from any variable is allowed: p-1)!²%p  Otherwise 12 bytes: ans−1)!²%ans  The great thing about "programming" in a calculator is that you can basically just enter formulas directly. Example usage in Bash for the "ans" case: echo "5" | qalc -t -f - "ans−1)! ²%ans"  Note that I added a space after the exclamation mark only because Bash otherwise tries to interpret "!²" as an "event". It's not actually required by qalc, which can be seen by for example creating this file: 5 (ans−1)!²%ans  …and then executing it with qalc -t -f test.txt. Other consoles or other ways of calling qalc than Bash might not have this problem. The calculation can also be entered in "interactive mode" by simply running qalc -t, entering the number and then entering the expression on the next input. This also works in the GUI program "Qalculate". ### Meta explanation: The output is 0 for non-prime numbers and a positive integer for prime numbers. I let this run in a loop for all numbers up to 10000 and it was always 1 for prime numbers, but I haven't checked whether that is guaranteed yet. This solution is based on this Labyrinth answer. I essentially just found something (qalc) that has all the parts of the formula as builtins instead of having to program all the parts myself on a lower level. The -t argument hides the interpreted calculation, so that the output of the example command looks like this: 5 1  …instead of like this: 5 = 5 rem(factorial(ans - 1)^2, ans) = 1  Reading the number in in qalc is difficult. It has a system of variables, but I haven't figured out how to set those in the CLI yet. In the GUI it's pretty easy. That's one of the main reasons why I also provided a solution with "ans". Inserting the number into the formula two times would mean modifying the "program", which is surely not allowed. There seems to be no way to execute multiple expressions non-interactively with qalc, except by reading in a file. In this case, I used - as a "file", which is StdIn, and used that only to store the input in ans, which is implicitly done by qalc. You could also use an actual file and use the number in that file as input. Or you could even say that ans is already the input of the "program", in which case the program is simply the 12 bytes seen above, or even any variable, then the 8 byte solution. ### Algorithm explanation: The Wikipedia article linked in the Labyrinth answer looks pretty confusing, but the principle is easy: (6-1)!²%6 = 1·1·2·2·3·3·4·4·5·5%6 = 1·1· 6 · 6 ·4·4·5·5%6 = 6 · something %6 = 0  This works because every non-prime number is the product of at least two factors that are smaller than that number. Prime numbers aren't, which leads to something like this: (5-1)!²%5 = 1·1·2·2·3·3·4·4%5 = 1·1·2·2·3·3·4·4%5 (no multiplication of those factors results in anything divisible by 5) = 1  The squaring is necessary in case there is only one prime factor and that occurs twice: (9-1)!²%9 = 1·1·2·2·3·3·4·4·5·5·6·6·7·7·8·8%9 = 1·1·2·2· 9 ·4·4·5·5·6·6·7·7·8·8%9 = 9 · something %9 = 0  I originally wrote this answer for TI-Basic: fPart((Ans-1)!²/Ans  That's just 10 bytes, but it fails on the input 13 already, due to floating point imprecisions in those large numbers (12!²=229442532802560000). So the only difference to an even/odd checker within the working range is 9 and it does not fulfil the criterion to work up to 255. For inputs above 42 it even crashed from an overflow (42!²>10¹⁰⁰). # GolfScript, 14 bytes ~.,{*.!+}*.*\%  Try it online! This outputs this version of Wilson's theorem, used in other answers to this question: (n-1)!² (mod n)  This outputs 1 if it is a prime and 0 if it is not. ~ # Push n ., # Range from 0 to (n-1) {*.!+} # Push block without executing * # Fold .* # Square, it could also be 2?, but for large values of n there would be an error message \% # Mod n  What the block does:  * # Multiply .! # Is it 0? + # Add 1 if it was 0 and 0 if it wasn't  This uses 3 bytes to avoid the 0, there are ways of removing it from the array using 2: ~.,(;{*}*.*\%  Try it online! The problem here is when the input is 1, in this case after removing the 0 we wouldn't have any number to multiply. # ArnoldC, 707 636 618 bytes Saved 71 89 bytes thanks to pppery! LISTEN TO ME VERY CAREFULLY f I NEED YOUR CLOTHES YOUR BOOTS AND YOUR MOTORCYCLE n HEY CHRISTMAS TREE k YOU SET US UP 2 HEY CHRISTMAS TREE l YOU SET US UP 1 HEY CHRISTMAS TREE p YOU SET US UP 1 GET TO THE CHOPPER l HERE IS MY INVITATION n LET OFF SOME STEAM BENNET k ENOUGH TALK STICK AROUND l GET TO THE CHOPPER p HERE IS MY INVITATION n I LET HIM GO k LET OFF SOME STEAM BENNET 0 KNOCK KNOCK p ENOUGH TALK GET TO THE CHOPPER k HERE IS MY INVITATION k GET UP 1 ENOUGH TALK GET TO THE CHOPPER l HERE IS MY INVITATION n LET OFF SOME STEAM BENNET k KNOCK KNOCK p ENOUGH TALK CHILL TALK TO THE HAND p HASTA LA VISTA, BABY  Try it online! Doesn't look like anyone's posted an ArnoldC answer here yet, and I thought the best way to respect the Terminator would be by writing an answer in his language. • Only 636 bytes as a function. – pppery Mar 19 at 21:15 • @pppery THANKS. ENOUGH TALK. HASTA LA VISTA, BABY. – user Mar 19 at 21:59 • Can be further reduced to 618 bytes by using the nonstandard output technique of a function outputting to STDOUT, which is allowed since functions may output via the same methods as full programs – pppery Mar 22 at 22:45 • @pppery Thanks again, I never thought anyone could golf in ArnoldC! – user Mar 22 at 23:05 # OCaml, 50 bytes fun n->List.(init (n-1) succ|>map((mod)n)|>mem 0);;  and it's almost idiomatic and readable. just sad that init begins at 0 and not 1, could have saved a lot on that :( # Knight, 35 bytes ;=y;=x+0P1;W&=z>x=y+1y%x y 0O&-xT!z  Try it online! ### Edit: Outgolfed by sampersand Rough. Prints true for primes, false or 0 for non-primes. # prompt for a number, coerce to integer ; = x + 0 PROMPT # loop counter ; = i 1 # Loop while x > y and x % y != 0 ; WHILE & (= cmp > x y) (% x y) : NOP # Output result. The - x 1 returns false for 1. : OUTPUT & (- x 1) (!cmp)  ## STATA, 62 bytes di _r(a) gl c=$a-1
forv b=2/$c{ if!mod($a,b') gl c=0
}
di $c  Ungolfed display _request(number) global maxtest =$number-1
forvalues counter=2/$maxtest{ if !mod($number,counter') global $maxtest = 0 } display$maxtest


This tests every integer from 2 to number-1 for divisibility. By printing number-1 as the output, it prints a 0 for an input of 1. Today I learned that STATA has truthy/falsey values. Previously I assumed I could only use (in)equalities in conditions. Note: this does not yet work in the online interpreter and is only valid in the proprietary STATA interpreter.

# Mathematica, 33 bytes or 61 bytes

Manipulate[PrimeQ[n],{n,1,255,1}]

<<PrimalityProving
Manipulate[ProvablePrimeQ[n],{n,1,255,1}]


As explained in the implementation documentation, PrimeQ[] is known to produce correct output for arguments less than 10^16 (though is widely believed, on heuristic arguments, to be correct for any input). (User Charles claims this bound can be increased to 2^64 ~= 10^19 in an answer here.) It tests for small primes, uses Miller-Rabin with bases 2 and 3, then uses a Lucas test. ProvablyPrimeQ[] uses a much slower testing procedure, Atkin-Morain (reference with further citations), but is known to be correct and can produce a certificate of primality or witness of compositeness, if desired. So, PrimeQ[] meets the challenge (255 is much less than 10^16), but ProvablyPrimeQ[] meets the specification "primality test" without reservation.

These wrap the PrimeQ[] call into a widget for user interaction. See the docs for a visual example. This widget provides a slider over the range 1 to 255 with unit increments. Next to the slider is a button to provide additional controls: a textbox for direct input and "playback" controls. It's interesting (at most, three times :-) ) to watch this widget iterate through the range.

• The rule for hardcoding are "If (and only if) your language is unable to accept any kind of user input" (emphasis mine). Mathematica can take user input, so I believe it needs to use that (see this answer for an example). – Sp3000 Sep 13 '15 at 12:50
• @Sp3000 : Huh. Did not know about Input[]. So, ..., is the local protocol to withdraw the whole solution, or keep the documentation that the solution you cite (and many others here) do not provably test for primality? – Eric Towers Sep 13 '15 at 23:55
• @Sp3000 : I now also perceive a bit of a gap between the rule you reference and the other rule "If your language is able to read from STDIN or accept command-line arguments". I certainly can't make Mathematica do that (and I think this negative capability is why I went the way I did). But I agree that Mathematica meets the description you have. Yet I can imagine settings where neither clause applies. – Eric Towers Sep 13 '15 at 23:59
• The rule you mention was indeed badly phrased, so I've rephrased it. However, the rule Sp3000 mentioned clearly stated that hardcoding is only allowed if there are no alternatives. Since Mathematica has Input[], your three snippets are invalid in its current form. – Dennis Sep 14 '15 at 3:59
• @Dennis : The third snippet receives user input, as described. – Eric Towers Sep 14 '15 at 6:33

# Mumps, 29

R J F I=2:1:J W:I=J J Q:J#I=0


Output is nothing if not prime, repeat the number if prime. [[ Looks kind of ugly, but I did this to save a carriage return, as carriage returns aren't echoed on user input. It was also easier to see the number out again than just a 1 or zero, that was confusing on longer queries, especially if they contained a '1' at the end. ]]

Test runs:

USER>R J F I=2:1:J W:I=J J Q:J#I=0
1234312343
USER>R J F I=2:1:J W:I=J J Q:J#I=0
12345
USER>R J F I=2:1:J W:I=J J Q:J#I=0
11141111114111


In these three runs, 12343, 12345 and 1114111 are the inputs (the 'R J' reads standard input into the J variable - but the carriage return is not echoed to the output).

As 12343 is a prime, it's echoed directly after the input; as 12345 is not prime, it sits alone. 1114111 is prime, but if I output just a single '1' to indicate prime, it would be much more difficult to tell if it was or not. I leave it up as an exercise to the reader to remember what was entered for the input number. :-)

[[ I wanted to output a character like '*', but then I would have needed to enclose that in quotes thereby making the answer longer. As would adding my own carriage returns...]]

# VBA, 160 bytes

For casuals only. Is MsgBox a STDOUT equivalent?

Sub p(n)
Dim t
For i = 2 To n - 1
If n / i = Int(n / i) Then t = True
Next
If t <> True Then
MsgBox n & " is truthy"
Else
MsgBox n & " is falsy"
End If
End Sub

• Your code can be significantly improved to Sub p() For j=2To n+1 t=IIf(n Mod j=0Or n<2,"falsy","truthy") Exit For Next Debug.? IIf(n=2,"truthy", t) End Sub 112 bytes – Anastasiya-Romanova 秀 Aug 21 '16 at 12:50

# Actionscript 3, 504 bytes

There are 265 bytes for the actual code. Nearly half the bytes come from the required xml file used by Adobe Debug Launcher to run the swf.

This is run by executing adl P-app.xml -- n to test n, followed by echo %errorlevel% to see the result.

<?xml version="1.0" encoding="UTF-8"?>

package{import flash.desktop.*;import flash.display.*;public class P extends Sprite{public function P(){var n=NativeApplication.nativeApplication;n.addEventListener('invoke',function(e){var p=e.arguments[0],i=2,c=p==1?0:1;while(c>0)c*=p%++i;n.exit(int(p==i));});}}}


# C++, 96 bytes

main(int c,char**a){int n=atoi(a[1]);for(c=2;c<n;c++){if(n%c==0){puts("0");return;}}puts("1");}


It the same method as the C program using trial division, it just reads the value in as command line arguement.

# Yorick, 20 characters

is_prime(read(,"i"))


read(,"i") reads an integer from STDIN and is_prime is the builtin prime tester of Yorick. Outputs 1 if prime and 0 otherwise.

## VBA Excel - 53 bytes

Golfed, to run in the immediate window :

t=false:for i=2 to j-1:t=(t Or j mod i=0):next:?not t


Performs a simple check for all values from 2 to j (the input)-1. If every division has a non-0 modulo, then it returns true (prime), otherwise it returns false (non-prime or error).

If you want to test this here is a larger code snippet that provides an inputbox for j:

j=inputbox(a):t=false:for i=2 to j-1:t=(t or j mod i=0):next:?not t


And for people that need it in a sub/function (ungolfed) :

function isprime(byval j as integer)  ' sanitize input to an integer.
for i=2 to j                        ' loop starting at 2 (so 1 or less is not prime).
t=(t or j mod i=0)                ' check if i is a divisor of j
next                                '      and add to existing return
isprime=not t                       ' if any i is a divisor then the return is false
end function                          '      so return the opposite (isprime)

• By the rules, if you have an input method you have to incorporate it. Also, little bug, you're returning TRUE for 1. In the spirit of your approach, I suggest turning the test around (and saving a couple of bytes): j=inputbox(7):t=j>1:for i=2 to j\2:t=t and 0<j mod i:next:?t – Joffan Jun 24 '16 at 5:42

# Hassium, 140 Bytes

use Math;func main(){n=Convert.toNumber(input());b=Math.floor(Math.sqrt(n));for(i=2;i<=b;++i)if(n%i==0){println("0");exit(0);}println("1");}


Lengthy:

use Math;
func main () {
n = Convert.toNumber(input());
b = Math.floor(Math.sqrt(n));
for (i = 2; i<= b; ++i)
if (n % i == 0) {
println("0");
exit(0);
}
println("1");
}


# not valid in Mathcad Prime Express (no symbolics)

n:=103   IsPrime(n)->


where -> is the symbolic evaluation operator

although

IsPrime(103)->


would be shorter still

edit 103 to taste

In response to the question from @Dennis the following might be helpful

Mathcad is, from a user perspective, a whiteboard in which you directly type in your expressions, programs, plots, etc and obtain the results either directly in the worksheet or export them (in some instances (eg, Excel) you can embed a "component" directly in the worksheet and access the application through the component. It also allows you mix text and expressions across the page(s) as well as down, making it almost a literate programming system.

In the above example, the input and output are all on the worksheet. All you need to do to change the 103 is click on it, delete the digits and add your own. If auto calculation is on, then Mathcad updates the output from the IsPrime function, otherwise choose the manual calculate option (which is simply pressing F9 in the case of Mathcad 15). Simples.

There are also file read and write functions if you want to do it the hard way, but Mathcad's interface makes it completely unnecessary for such a simple task.

See this link https://www.ptcusercommunity.com/message/420452#420452 for an example of an over-the-top means of finding the middle value of a vector (list). What you see is what I typed in or what Mathcad computed in response. If I were to edit the worksheet to, say, change v1's value from seq(6)+11 to seq(9)+20, Mathcad would almost instantly change the output from the "augment" expression to show the new value of v1 together with its corresponding indices. I'd have to manually rearrange the v2 expressions to make room for the new v1 but that's as simple as dragging the mouse around the affected expressions, which selects them, and then dragging the expressions to the new location. Easy. Even I can do it!

• Is there no way of obtaining user input in Mathcad? – Dennis Sep 12 '15 at 1:28
• That depends upon what you mean by "obtaining user input". I've added a bit more text to my original post to help clarify how a typical Mathcad might change the number to be tested - just edit it directly on the Mathcad "worksheet" and Mathcad will update the result. – Stuart Bruff Sep 12 '15 at 8:23
• Please make sure you add in the byte count to the title of your post so that it can register on the leader board. Check the question on how to format it. – rayryeng Sep 12 '15 at 16:28
• Do you which algorithm is used by IsPrime? Are you sure it's not a probabilistic one like Miller-Rabin? – Martin Ender Sep 14 '15 at 9:45

## Burlesque, 7 bytes

blsq ) 71fC
{71}
blsq ) 71fCL[1==
1
blsq ) 72fC
{2 2 2 3 3}
blsq ) 72fCL[1==
0


fC does a prime factorization. If the length of the resulting block is 1, then we have a prime. Note that this isn't as fast as a Miller-Rabin or similar obviously :p. With the next planned release this will be two bytes.

Probably not the shortest program:

 #
W
I
P
v
>~1=
~
0
=


Another possible program is, 30 bytes:

#WIP>v~0=
~
1
=


Information:

• # = Starting point, pointer direction is to the right
• W = User input, directly adds this to the stack
• I = If-statement, or is equal to
• P = If the stack is prime
• v = If false, assign the pointer direction to the right
• > = If true, assign the pointer direction to the bottom
• ~ = Reset the stack
• 0 / 1 = Assign the stack to 0 / 1
• = = Print the result of the stack

The following paths are executed in this program:

• If W = prime, path = WIP~1=
• If W != prime, path = WIP~0=

This is a 2D esolang I created, which looks a bit like a magic square. This is a programming language in it's early stage, so a lot of functions aren't implemented yet. Also, a lot of bugs might occur, if you find a bug, please report it.