Iterating over some huge search space in an essentially sequential manner is generally not going to be nearly performant as simply selecting an odd number at random. You could try using a generating polynomial instead such as f(x) = x^2 + x + 41 but even that isn't going to help much in the long run. (There are Diophantine equations which one day may prove useful for generating random primes however AFAICT finding efficient solutions is still currently considered a hard problem.)