78 questions linked to/from Is this number a prime?
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### Orientation Oriented Programming

Write a program for a specific language that in different orientations performs different tasks. Your code should have at least two non-empty lines and at least two non-empty columns and should ...
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### 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 ...
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### Implement bag operations

A bag, also called a multiset, is an unordered collection. You can call it a set that allows duplicates, or a list (or an array) that is not ordered/indexed. In this challenge, you are asked to ...
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### 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 definition ...
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### I want 8 bits for every character!

This is the reverse of this challenge. Given an encoded list of codepoints and the characters used to encode it, you need to decompress it to its original string. For example, given the encoded list <...
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### Convert a decimal integer to binary only using arithmetic operators

There are 10 types of people in the world, those who understand binary and those who do not. Where are you? Let's see! Challenge Your task is to convert a decimal integer to binary, only using a ...
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Intro Reverse and add is as simple as it sounds, take n and add it to its digits in reverse order. (e.g. 234 + 432 = 666). If you apply this process repeatedly ...
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### Parse a two-dimensional syntax

Background Alice and Bob are creating a golfing language to win every single PPCG challenge. Alice wants to make a two-dimensional language, like ><>, but Bob prefers a prefix-infix syntax like in ...
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### A regex to match three consecutive integers iff the third integer is the sum of the first two

Write a regular expression which matches a given string consisting of three non-negative, space-separated integers if and only if the last integer is the sum of the previous two. Answers may be for ...
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### Build a golfing language with me

A lot of PPCG users helped with the creation of this challenge, both in chat and the Sandbox, specifically Martin Ender, AdmBorkBork, Emigna and user202729 Our community has found it necessary to ...
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### GolfScript, CJam, or Pyth? [duplicate]

Which language usually produces shorter golfed code: Pyth, CJam or Golfscript? In asking this, I do not mean which has a prettier syntax or which has the most useful commands, I mean overall, which ...
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### Generating Fermat primes

Given a number n, print the nth prime Fermat number, where the Fermat numbers are of the form 22k+1. This code should theoretically work for any n (i.e. don't hardcode it), although it is not expected ...
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### The Most Wanted Prime Numbers

Output a sequence of all the primes that are of the following form: 123...91011...(n-1)n(n-1)..11109...321. That is, ascending decimal numbers up to some ...
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### Counting Abelian groups of a given size

Background Last time, we counted groups of a given size, which is a non-trivial problem. This time, we'll only count Abelian groups, i.e., groups with a commutative operation. Formally, a group (G, ∗) ...
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