It was not really meant to be a heavy duty prime number finder but something compatible with my rather meagre mathematical skills. And after all, Eratosthenes never had to worry about going out of bounds in 250BC :-) On my ancient hardware I don't ask it to go beyond 10000000 as I don't have all day while it fills in all the multiples of 2 etc.

FWIW, I am still trying to get my head around your method. I downloaded and ran it and was very impressed with it's speed on a 250MHz UltraSPARC, but I don't quite understand it yet. I'll get there eventually.

Cheers,

JohnGG