Regular expressions are a powerful tool that can be used in different programming languages. A regular expression in Perl, /^1?$|^(11+?)1+$/, can be used to check if a number is prime or not. Although skeptical at first, someone tested the regular expression in Ruby and found that it also works in that language. The regular expression consists of two parts, with the second part being the most complex. Ultimately, the regular expression successfully identifies prime numbers by eliminating even numbers except 2 and testing each odd number through a process of backtracking. Despite someone’s initial doubts, the regular expression is indeed an effective solution.
https://www.noulakaz.net/2007/03/18/a-regular-expression-to-check-for-prime-numbers/