Demystifying The Regular Expression That Checks If A Number Is Prime

The regex ^.?$|^(..+?)\1+$ can identify non-prime numbers in unary representation by matching 0-1 characters or finding factors through repeating substrings. It uses capturing groups, backreferences, and quantifiers to check divisibility. While not efficient, it's an interesting regex application. The article provides code examples in multiple languages and explains the regex's components step-by-step.