343
Oh boy what a beautiful regex. I'm sure it does something logical and easy to understand.
(lemmy.world)
^.?$|^(..+?)\1+$
Matches strings of any character repeated a non-prime number of times
Regular expressions in general, and automata theory, sure you should know about that. But a specific extended regex language like here? That's like saying you're shit at coding if you can't do .