Slick ;)

Please which language?
Don't post an issue before being sure of your code.
361 is not prime. I think you could better your prime numbers algo, sorry to say that: maybe it is fast but it is wrong (361 = 19 * 19).
If you want no timing out your algo for primes must be faster.

Wrong testcases:
Test.assert_equals(gap(8,300,400), [359, 367])

361 is prime and in between [359,367]

Also submission times out, but locally I can generate 10000 prime numbers in under 1 second.

must be the server? I was getting these errors every time I submitted a new version of my solution… then it magically started working after I tried some code copy/pasted from this discussion. All my previous attempts work now 0_o

I'm getting unknown error