78 questions linked to/from Is this number a prime?
2k views

### Recognize most smaller primes with a regex

This time, you are working on a regex. Your regex is meant to approximately full-match the base-10 representations of primes $0 \le p < 1000$, while ignoring any non-numeric string or composite ...
• 3,849
42k views

### Hard code golf: Regex for divisibility by 7

Matthias Goergens has a 25,604-character (down from the original 63,993-character) regex to match numbers divisible by 7, but that includes a lot of fluff: redundant parentheses, distribution (...
• 2,771
365 views

### Primes, as efficiently inefficient as possible [duplicate]

Write a program that tests if a number n is prime by checking that none of the integers between 2 and ...
• 7,387
1k views

### 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 ...
• 42.7k
894 views

### Crazy Librarian's Interesting Prime Permutation Index Number Generator

You saved the day with your prime sequence code, and the math teacher loved it. So much so that a new challenge was posed to the librarian (a/k/a, your boss). Congratulations, you get to code the ...
• 43.4k
212 views

### Prime decimal representations of prime binary numbers [duplicate]

Problem Statement: Consider a number n in base-10. Find the smallest base-10 integer i greater than ...
3k views

### 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 ...
• 23.9k
433 views

### 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, ∗) ...
• 210k
606 views

### 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 ...
• 7,898
1k views

### 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 ...
3k views

### 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 ...
• 449
527 views

### Peel the potato

This is a potato: @@ @@@@ @@@@@@ @@@@@@ @@@@ @@ More generally, a size N potato is defined as the following shape: If N is even, it is 2 centered ...
• 341
2k views

### 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 ...
• 2,530
805 views

### Unrestricted Languages

One of my favorite types of challenges on this site are restricted-source challenges. These challenges impose a computer tractable restriction that the sources of potential answers must pass. I like ...
• 98.8k
1 vote