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# Questions tagged [number]

A competition to solve a particular problem through the usage and manipulation of numbers.

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### 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 ...
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### Fibonacci function or sequence

The Fibonacci sequence is a sequence of numbers, where every number in the sequence is the sum of the two numbers preceding it. The first two numbers in the sequence are both 1. Here are the first ...
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### Largest Number Printable

Your goal is to write a program that prints a number. The bigger the number, the more points you'll get. But be careful! Code length is both limited and heavily weighted in the scoring function. Your ...
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### crossed out 44 is still regular 44 ;(

Introduction On March 24th, 2015 @isaacg golfed his Pyth answer from 44 to 42 bytes. Since a crossed out 44 (44) looks a lot like a regular 44, @Optimizer made the following comment: striked out ...
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### Count up forever

Write a program that counts up forever, starting from one. Rules: Your program must log to STDOUT or an acceptable alternative, if ...
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### Sum of all integers from 1 to n

I'm honestly surprised that this hasn't been done already. If you can find an existing thread, by all means mark this as a duplicate or let me know. Input Your input is in the form of any positive ...
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### Say What You See

The "Look and say" or "Say what you see" sequence is a series of numbers where each describes the last. ...
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### It's Hip to be Square

Challenge So, um, it seems that, while we have plenty of challenges that work with square numbers or numbers of other shapes, we don't have one that simply asks: Given an integer ...
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### Base Conversion With Strings

Introduction We've have a few base conversion challenges here in the past, but not many designed to tackle arbitrary length numbers (that is to say, numbers that are long enough that they overflow the ...
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### XOR multiplication

You goal is to implement the operation of XOR (carryless) multiplication, defined below, in as few bytes as possible. If we think of bitwise XOR (^) as binary ...
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### Find the number in the Champernowne constant

Introduction In base 10, the Champernowne constant is defined by concatenating representations of successive integers. In base 10: 0.1234567891011121314151617... ...
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### Determine the position of a non-negative number in the infinite spiral

Definition The infinite spiral used in this question has 0 on the position (0,0), and continues like this: ...
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### The Versatile Integer Printer

Write a piece of code that is executable in at least three different languages. The code must output the integer 1 in language number one, ...
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### Numbers with Rotational Symmetry

Given an integer, output a truthy value if it is the same upside-down (rotated 180°) or a falsy value otherwise. 0, 1, and ...
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### Balanced Ternary Converter

Credits for the challenge idea go to @AndrewPiliser. His original proposal in the sandbox was abandoned and since he has not been active here for several months, I have taken over the challenge. ...
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### Different Way Forward

Given a list of integers produce a Forward Difference at a specified order/depth. For the list of integers: (10, 18, -12, 4, 8, -3, -5, 67, 9, 14) The Forward ...
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### How high can you count?

Challenge: Your task is to write as many programs / functions / snippets as you can, where each one outputs / prints / returns an integer. The first program must output the integer ...
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### The Coin Problem

Background The official currency of the imaginary nation of Golfenistan is the foo, and there are only three kinds of coins in circulation: 3 foos, 7 foos and 8 foos. One can see that it's not ...
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### Generate a Kolakoski sequence [duplicate]

Definition1 A Kolakoski sequence is a self-describing infinite sequence {kn} of alternating blocks of 1's and 2's, given by the following rules: k0 = 1 kn = the length of the (n+1)'th ...
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### What is the smallest positive base 10 integer that can be printed by a program shorter (in characters) than itself?

I think the question as above is clear, but just in case: Write a full program (not just a function) which prints a positive base 10 integer, optionally followed by a single newline. Qualifying ...
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### Output the sign

Given a number N, output the sign of N: If N is positive, output 1 If N is negative, output -1 If N is 0, output 0 N will be an integer within the representable range of integers in your chosen ...
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### Count trailing truths

Inspired by, and in memory of, my dear friend and colleague, Dan Baronet, 1956 – 2016. R.I.P. He found the shortest possible APL solution to this task: Task Given a Boolean list, count the number of ...
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### Golf a number bigger than TREE(3)

The function TREE(k) gives the length of the longest sequence of trees T1, T2, ... where each vertex is labelled with one of k colours, the tree Ti has at most i vertices, and no tree is a minor of ...
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### Outputting ordinal numbers (1st, 2nd, 3rd)

I would like to generate (as a return result of a function, or simply as the output of a program) the ordinal suffix of a positive integer concatenated to the number. Samples: ...
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### Notcalc (Calculate the wrong answer)

Goal: Given two natural numbers (integers from 0 to infinity), output a number that is not the sum of those numbers, but is a natural number. Example solutions (TI-Basic): ...
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### I reverse the source code, you negate the input!

Blatant rip-off of a rip-off. Go upvote those! Your task, if you wish to accept it, is to write a program/function that outputs/returns its integer input/argument. The tricky part is that if I ...
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### Generate Monday Numbers

Monday numbers, as defined by Gamow in this question over on Puzzling, are positive integers N with the following three properties: The decimal representation of N does not contain the digit 0 The ...
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### Natural construction

The natural numbers including 0 are formally defined as sets, in the following way: Number 0 is defined as the empty set, {} For n ≥ 0, number n+1 is defined as n ∪ {n}. As a consequence, n = {0, 1, ...
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### Turn an integer n into a list containing it n times [closed]

Given an integer n as input, return a list containing n, repeated n times. For example, the ...
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### Mixed Base Conversion

Background Most people on here should be familiar with several base systems: decimal, binary, hexadecimal, octal. E.g. in the hexadecimal system, the number 1234516 would represent ...
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### Return each number from a group of numbers

The challenge The program must return all numbers included into a group (comma and hyphen separated sequence) of numbers. Rules s is the sequence string; all ...
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### Implement t9-like functionality

Your challenge today is to implement a t9-like functionality. You will implement a function that will only have 2 parameters. You will receive 1 phone number in a string and the content of a text ...
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### Largest number in ten bytes of code [closed]

Your goal is to print (to the standard output) the largest number possible, using just ten characters of code. You may use any features of your language, except built-in exponentiation functions. ...
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### Print all integers

Write a program or function which will provably print all integers exactly once given infinite time and memory. Possible outputs could be: ...
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### Encode an integer

Given positive integer n > 2. We convert it to an array as follows: If it is equal to 2 return an empty array Otherwise ...
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### Multiply two numbers

Input: Two decimal integers. These can be given to the code in standard input, as arguments to the program or function, or as a list. Output: Their product, as a decimal integer. For example, the ...
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### Spell out numbers in French

There was a challenge to convert a number to its numeral in English, but that was too straightforward. Given a number 0–100, your task is to output the corresponding numeral in French. The French ...
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### Flipping pancakes

In pancake sorting the only allowed operation is to reverse the elements of some prefix of the sequence. Or, think of a stack of pancakes: We insert a spatula somewhere in the stack and flip all the ...
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### List Prime Numbers [duplicate]

Introduction Prime numbers are simple, right? Well, now you get your chance to find out! Challenge You must write a program or function that takes an input n and ...
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### Prime factors buddies

Given an integer N > 1, output all other numbers which prime decompositions have the same digits as the prime decomposition of ...
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### Dames, do some math!

The order of operations, PEMDAS, is a basic rule in mathematics telling us which order operations should be performed: "Parentheses, Exponents, Multiplication and Division, and Addition and ...
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### New Order #1: How does this feel?

Introduction Putting all positive numbers in its regular order (1, 2, 3, ...) is a bit boring, isn't it? So here is a series of challenges around permutations (reshuffelings) of all positive numbers. ...
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### Compute the number of ways how you can express a number as a sum [closed]

For a given natural number n, compute the number of ways how one can express n as a sum of positive natural numbers. For example,...
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### Hyperprogramming: N+N, N×N, N^N all in one

Write a program that takes in a number N from 1 to 9 inclusive. In its native form your program should output N+N. E.g. output 2 if N is ...
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### Generate Dennis Numbers

This challenge is a tribute to PPCG user Dennis for winning the robbers' part of The Programming Language Quiz. Looking at Dennis' PPCG profile page we can see some pretty impressive stuff: He ...
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### No strings (or numbers) attached

If you like this, consider participating in: The Official Dyalog APL 2016 Year Game The monthly Dyalog APL 2017 Code Golf Challenge Make 12 snippets/expressions, in the same language, that result in ...
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### Print 0 to 100 without 1-9 characters

Print integers 0 to 100 (inclusive) without using characters 123456789 in your code. Separator of numbers can be comma or white space (by default <blank>, <...
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### Compute the Kolakoski sequence

This is a repost of an old challenge, in order to adjust the I/O requirements to our recent standards. This is done in an effort to allow more languages to participate in a challenge about this ...
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### Is this number evil?

Introduction In number theory, a number is considered evil if there are an even number of 1's in its binary representation. In today's challenge, you will be identifying whether or not a given number ...
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