Quote:
Originally Posted by TTn
PS I notice k is seldomly prime, for Riesel primes.
Does anyone know the mechanism for this?

If p divides k, then p does not divide k*2^n1. This means that N=k*2^n1 is prime with probability k/phi(k) * 1/ln(N) instead of probability 1/ln(N).
For k<100 with k*2^n1 prime, this moves the probability that k is prime from 1 in 4 to 1 in 7; for k<1000, the probability of k prime moves from 1 in 6 to 1 in 11; for k<10000, the probability moves from 1 in 8 to 1 in 16.