Fixed off-by-one error.
2 was not being considered as prime number, by 1 was. Fixed by manually
setting 2 as first prime, then continueing with odd candidates.
Solution to problem 10.
It's a bit slow, it can probably be optimized further.
Removed storing primes.
Upper bound does not need to be set for each i.
Upper bound is ceiling(sqrt(candidate)) effectively for each candidate, so setting it as that removes a few operations.