since the GCW Sieve is running on a set of bases b = 13, 25, 29, 41, 47, ... it is clear that the GCW LLR will also start on these bases.
My question is: what is the reason for using exactly this set of bases? Is it just random because one has to start somewhere, or is there a mathematical reason, e.g. is it expected to find more primes on those bases than on other ones?
Is it also planned to go to other bases b on a long term?