Your primes variable does not really do what you'd probably hope it to do. Your inner loop (the one over j) and primes vector do quite a lot of work which is superfluous, discarded soon after used, and not really useful.

Found it. Thanks!

Avoid using loops.

Not an issue. Something's wrong with your code.

Post your code using markdown formatting and marking your post as having spoiler content then.

Sample tests + my own with bigger values all pass.

That's weird, I've tried with a less optimized code and it passed, are you sure you don't have an infinite loop somewhere?