"At least one letter character at the beginning"

Thanks for your feedback!

Agree, definitely nice as it makes you think about the nature and sequence of primes (these abstract mathematical patterns can emerge themselves in the real-world quite often). Getting to know primes better is definitely a good exercise.

As for AntraxMiope, are you still stuck? If so, think about how to speed up your algorithm for prime checking.

That's great. All my solutions are being rejected (Timeout or memory error).
Could you give some pointers?

Fixed. Could you tell me if it works for you now? Thanks for the feedback!

Test Cases added, thanks to @ZozoFouchtra. I appreciate your feedback, thank you!