The Non-Prime Regex is in the cross-section of two of my interests

Roughly 4.5 years ago I shared in this blog my interest for recreational mathematics. Yes, I’m that kind of geek.

I’ve been keeping up with my hobby throughout these years.

I also have confessed my love for regular expressions.

Hence, I was delighted when these two crossed paths in Matt Parker’s fantastic Youtube channel last week on his video How on Earth does ^.?$|^(..+?)\1+$ produce primes?

In it, Parker walks through how the regex /^.?$|^(..+?)\1+$/ can tell if a number n is prime, when the string "1" * n (string “1” written n times) is passed through it.

Illya Gerasymchuk has written a brilliant blog post that really goes in depth to the topic in Demystifying The Regular Expression That Checks If A Number Is Prime so I won’t repeat the steps of the blog post or the video here.

I just wanted to let you know that these two absolutely incredible pieces exist so you can discover the same joys of life that I do.