prime numbers

Does anyone know any usefull routines, for proving primes of the form 2^p-1.
These are othwise known as Mersenne primes, since the exponent p is always prime too.

To learn more about them see:
http://mersenneforum.org/

Or see my section here:
http://www.mersenneforum.org/forumdisplay.php?f=16

math.wolfram.com probably has lots of info on this, although they don't usually carry algorithms in any useful form (ie. code).

Yes wolfram is a great resource, although incomplete on many properties about these numbers, especially code. Thanks!

There was a prime number contest last year in the contests section. And loads of previous posts on prime numbers, probably something around in one of those??
I think I recall Wossname making an excellent proggy to do them??