As a footnote to my previous message, (p - 1)! ~ -1 mod p whenever p is prime (Wilson's theorem). This follows immediately from the general rule that I gave. - Mark - -- Mark Chen chen at netcom.com 415/329-6913 finger for PGP public key D4 99 54 2A 98 B1 48 0C CF 95 A5 B0 6E E0 1E 1D