Questions tagged [primes]

For challenges about identifying and manipulating prime numbers

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26
votes
6answers
2k views

Concatenating Primes

Challenge: You are given a string containing only digits. Your task is to output the minimum number of primes which must be concatenated to form the string. If this is impossible, output ...
19
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28answers
3k views

Calculate prime gaps

Finding primes is a programming rite of passage and very frequently a first serious program someone crates (usually with trial division). But primes alone are already worn out. A next far more ...
19
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29answers
2k views

Cops and Robbers: Redacted Primality (Cops' Thread)

This challenge was originally sandboxed by Magic Octopus Urn; I adopted and posted it with his permission. This is the cops' thread. The robbers' thread is here. The challenge Step One: Write a ...
14
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33answers
2k views

How many unique primes?

One way to represent a natural number is by multiplying exponents of prime numbers. For example, 6 can be represented by 2^1*3^1, and 50 can be represented by 2^1*5^2 (where ^ indicates exponention). ...
28
votes
13answers
3k views

Is it a turtle prime?

As we all know, it's turtles all the way down. But is it primes all the way down too? A number is considered a "turtle-prime" if it satisfies the following conditions: ...
22
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22answers
2k views

Get thee behind me Satan-Prime!

Satan-Primes who are they? they are Primes containing 666 these are Satan-Primes:...
18
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14answers
2k views

Pretty Smooth Moves

In arithmetic, an n-smooth number, where n is a given prime number, is mathematically defined as a positive integer that has no prime factors greater than n. For example, 42 is 7-smooth because all ...
18
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21answers
1k views

Excessive Integers

For a positive integer n with the prime factorization n = p1^e1 * p2^e2 * ... pk^ek where ...
17
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6answers
1k views

Primes of Ulam's Spiral

Ulam's spiral is a truly fascinating, yet puzzling, topic in mathematics. How it works in detail can be found here, but a short summary can be explained as so: I start off by writing a one, then I ...
12
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14answers
1k views

Composite Number Sequences

Composite Number Sequences Inspired by this question Given a positive integer n, your code must output the first n composite numbers. Input / Output You may write a program or a function. Input is ...
41
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15answers
5k views

Determine whether a number is 2017-friable without primes in your source code

Out of all the years I've been making this challenge, 2017 is the first year that's been a prime number. So the question will be about prime numbers and their properties. Your task is to produce a ...
27
votes
21answers
1k views

Primenary Strings

A Primenary (binary-prime) string is one which, when written as a binary grid, every row and column has a prime total. That's quite a vague explanation, so let's break it down with a worked example.....
24
votes
9answers
2k views

The Solitude of Prime Numbers

Recently I read the novel "The Solitude of Prime Numbers" where the main characters are somewhat compared to twin prime numbers ("always together, but never touching"). A twin prime is a prime ...
22
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32answers
1k views

A prime test that's LITERALLY prime

Write a program that will test the primality of a specified number, and give the output as a Boolean value (True is prime). Your prime test can (but doesn't have to) be valid for the number 1. Here'...
19
votes
3answers
750 views

A Mapping of Primes

Recently, I have found a bijective mapping f from positive integers to finite, nested sequences. The purpose of this challenge is to implement it in the language of your choice. The Mapping Consider ...
17
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11answers
2k views

Find Recursively Prime Primes

The Recursively Prime Primes is are sequence of primes such that p(1) = 2 p(n) = the p(n-1)th prime Here is an example of how one might calculate the 4th ...
16
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31answers
1k views

Recover the power from the prime power

It seems that many people would like to have this, so it's now a sequel to this challenge! Definition: a prime power is a natural number that can be expressed in the form pn where p is a prime and n ...
16
votes
2answers
3k views

Prime Nerd Sniping Pattern

Longest day of the year - here's something to waste the extra time... Overview Note this is not a popularity contest and not a graphical output challenge - you are only required to output a string ...
15
votes
13answers
993 views

Transposed, primes, oh my!

The task is simple: your program reads an integer as an input, and prints whether it is a prime or not. You can print "yes/no", "true/false" or anything what unambiguously identifies the result. The ...
15
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30answers
4k views

Goldbach's conjecture

Write a program that prompts the user for an even integer greater than 2. Given Goldbach’s conjecture that every even integer greater than 2 can be expressed as the sum of two primes, print out two ...
12
votes
7answers
4k views

Determine if a number is prime without using arithmetic [duplicate]

Write a program which determines if a given number is prime. The catch: No digits or arithmetical operators. This means: No digits from 0 to ...
11
votes
4answers
462 views

Calculate the p-adic norm of a rational number

Calculate the p-adic norm of a rational number Write a function or a program, that takes 3 integers m,n,p (where p is a ...
11
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12answers
1k views

List all palindromic prime dates between 0000-01-01 and 99999-12-31

You know what a palindrome, a prime and a date are. Your task is to list all dates in 100 thousands of years that fulfill all three characteristics. Nevermind anything but the numbers, use the ...
8
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27answers
3k views

Generate Sexy Primes

Sexy Primes are pairs of numbers (n, m) such as n and m both are prime, and ...
4
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20answers
2k views

Illiteral Prime numbers [duplicate]

Your challenge is to write a program (full program, not a function), that will take an integer and output all prime numbers up to (including) the given integer. Output is any readable list containing ...
27
votes
20answers
3k views

Is it a Chen prime?

A number is a Chen prime if it satisfies two conditions: It is prime itself Itself plus two is either a prime or a semi-prime. A prime is a number where it has exactly two divisors and those ...
24
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28answers
2k views

Magnanimous numbers

Given an positive integer as input determine if it is a magnanimous number. A magnanimous number is a number such that any insertion of a + sign between any two ...
23
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11answers
1k views

Find the nth Fibohexaprime

The challenge this time is to find the nth Fibohexaprime. The definition of a Fibohexaprime is as following: We first observe a list with Fibonacci numbers: ...
20
votes
9answers
973 views

Novel Prime Factors of Repunits

The Background Folks were talking prime factorization in chat and we found ourselves talking about repunits. Repunits are a subset of the numbers known as repdigits, which are numbers consisting of ...
18
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26answers
3k views

Cops and Robbers bowling (Cops)

Cops' Thread In this challenge, your goal is to write a function that accepts a integer N, and that function will return the first ...
18
votes
4answers
1k views

Crazy Librarian's Arithmetic Sequence of Primes

Well, the librarian caught you cheating at your job by using your sorting algorithm, so now you're being punished. You've been ordered to create some code so the librarian can impress the object of ...
17
votes
31answers
2k views

Finding Not-Quite-Prime Numbers

Your challenge, should you chose to accept it, is to code-golf a function that returns true or false (or some similar meaningful representation of yes and no) if a number meets the following criteria: ...
17
votes
7answers
2k views

Primes in Different Bases

Challenge: You are given a base 10 number. For each base from 10 counting down to base 2: Take the original input number as a base 10 string, and remove any digits of the number which are invalid ...
14
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27answers
2k views

Prime or highest factor

Challenge: Given an array of non-negative whole numbers numbers in the range of 0 to Infinity, Check whether all of them are primes or not. (You can take input as ...
14
votes
14answers
2k views

Generate strong primes [duplicate]

In number theory, a strong prime is a prime number that is greater than the arithmetic mean of the nearest prime above and below (in other words, it's closer to the following than to the preceding ...
13
votes
32answers
2k views

Recover the prime from the prime power

Definition: a prime power is a natural number that can be expressed in the form pn where p is a prime and n is a natural number. Task: Given a prime power pn > 1, return the prime p. Testcases: <...
10
votes
24answers
2k views

Cops and Robbers bowling (Robbers)

Robbers' Thread In this challenge, your goal is to crack some code written by the Cops (their code is here) by modifying it. You have cracked their code if: Your modified code has a maximum ...
10
votes
16answers
1k views

Do we share the prime cluster?

The prime cluster of an integer N higher than 2 is defined as the pair formed by the highest prime strictly lower than N and the lowest prime strictly higher than N. Note that following the ...
9
votes
6answers
911 views

Calculate the Kronecker symbol

Relevant links here and here, but here is the short version: You have an input of two integers a and b between negative ...
9
votes
14answers
697 views

Cops and Robbers: Redacted Primality (Robbers' Thread)

This is the robbers' thread. The cops' thread is here. Your challenge is to take an uncracked submission from the cops' thread and try to find the original unredacted program. Please comment on the ...
8
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3answers
1k views

List prime-factorized natural numbers up to N in ascending order

For a given n list prime factorization of all natural numbers between 1 and n in ascending ...
8
votes
7answers
1k views

Recursive Prime Factorization

Your job is to take the prime factors of a number taken from input (omitting any exponents equal to 1) then take the prime factors of all of the exponents, and so on, until no composite numbers remain;...
8
votes
6answers
2k views

Code-Challenge:The Nearest Prime

Challenge In this task you would be given an integer N you have to output the nearest prime to the integer. If the number is prime itself output the number. The input N is given in a single ...
8
votes
1answer
1k views

Palindromic prime

I'm solving task, where: Input: A number as an integer. Output: The closest greater palindromic prime as an integer. I would appreciate hints how to make my solution shorter. Or directions if ...
8
votes
3answers
425 views

Counting Eisenstein primes

Introduction Eisenstein integers are complex numbers of the form a+bω Where a,b are integers, and ...
7
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7answers
1k views

Nth K-Ugly Number

Write the shortest code in any language of your choice to find the Nth K-ugly number. A K-ugly number is a number whose only prime factors are the prime numbers <= K. This K-ugly number is ...