I know of the up and down counters, I was wondering is there was a way to have a counter count only prime numbers in binary. Instead of going 1...2...3...4...it would go 1...3...5...7 ect. I was thinking of having maybe one of the flip-flops connect from the Reset to a Qnot so it would produce a zero rather than a 1. Or maybe for the up counter circuit, flip one of the AND gates. I am spewing out ideas... I am just wondering if its possible and how, what would have to be done to the FLip FLops..or rather the Logic Gates?