The Great Internet Mersenne Prime Search reports that they’ve probably found the 44th Mersenne prime:
“On September 4, 2006, a computer reported finding the 44th known Mersenne prime. Verification will begin shortly, probably taking a week or so to complete. If it is verified, this will be GIMPS’ tenth prime!”
A nice little introduction to Mersenne primes and Mersenne numbers in general can be found at Wikipedia.
