^.?$|^(..+?)\1+$
<answer>
Matches strings of any character repeated a non-prime number of times
You are viewing a single thread.
View all comments 3 points
Empty input Or input of exactly 1 character Or input of at least 2 characters, followed by at least 1 something (idk what \1 matches)
Did I get it (almost)?
1 point
*
\1 is group 1 which is inside (), so second part is repeated 2 or more times of 2 or more char.