78 questions linked to/from Is this number a prime?
194k views

### "Hello, World!"

So... uh... this is a bit embarrassing. But we don't have a plain "Hello, World!" challenge yet (despite having 35 variants tagged with hello-world, and counting). While this is not the most ...
18k views

### List of primes under a million

This is my first code golf question, and a very simple one at that, so I apologise in advance if I may have broken any community guidelines. The task is to print out, in ascending order, all of the ...
35k views

### Implement a Truth-Machine

A truth-machine (credits goes to this guy for coming up with it) is a very simple program designed to demonstrate the I/O and control flow of a language. Here's what a truth-machine does: Gets a ...
47k views

### Shortest infinite loop producing no output

Your task is to create the shortest infinite loop! The point of this challenge is to create an infinite loop producing no output, unlike its possible duplicate. The reason to this is because the code ...
3k views

### Primes with prime bit-counts

Task Find all the non-negative integers up to and including a given non-zero positive integer n, that are prime and the count of 1's and ...
14k views

### (-a) × (-a) = a × a

We all know that $(-a) \times (-a) = a \times a$ (hopefully), but can you prove it? Your task is to prove this fact using the ring axioms. What are the ring axioms? The ring axioms are a list of ...
6k views

### Divisibility test

Task Given two strictly positive integers n and d as input, determine whether n is evenly divisible by d, i.e., if there exists an integer q such that n = qd. You ...
4k views

### Is it a Mersenne Prime?

A number is a Mersenne Prime if it is both prime and can be written in the form 2n-1, where n is a positive integer. Your task is to, given any positive integer, determine whether or not it is a ...
76k views

### 1, 2, Fizz, 4, Buzz

Introduction In our recent effort to collect catalogues of shortest solutions for standard programming exercises, here is PPCG's first ever vanilla FizzBuzz challenge. If you wish to see other ...
65k views

### Golf you a quine for great good!

Using your language of choice, golf a quine. A quine is a non-empty computer program which takes no input and produces a copy of its own source code as its only output. No cheating -- that means ...
4k views

### Generating a random alphanumeric string of length N

What is the shortest way of generating a random string with a given length and with only alphanumeric characters allowed? example of a random string: with N = 9 output would be ...
28k views

### Tips for golfing in Java

Are there any useful shortcuts that can be used in Java? As shown below, import already adds at least 17 characters to a program. ...
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 ...
3k views

### 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 <...
### Compute the minimum $a(n)>a(n-1)$ such that $a(1)+a(2)+\dots+a(n)$ is prime (OEIS A051935)
Background Consider the following sequence (A051935 in OEIS): Start with the term $2$. Find the lowest integer $n$ greater than $2$ such that $2+n$ is prime. Find the lowest integer $n'$ ...