3. Say, because of Mersenne numbers' special structure (sexy, as you call it, I call it nifty), it gives them some equally nifty properties. Coincidentally, humans use binary computers, so testing Mersenne numbers happens to be really FAST. :-D 2^p-1 is easier to test for primality than any (???) other structure of number in the same sort of size range (# of digits, etc). Isn't it? STL
