Pratt Certificates of Primality

http://demonstrations.wolfram.com/PrattCertificatesOfPrimality/ The Wolfram Demonstrations Project contains thousands of free interactive visualizations, with new entries added daily. A prime number p can be proved prime by exhibiting all the prime factors of p - 1 together with a witness w such that w^p - 1=1 (mod p) but w^(p - 1) / qa1 (mod p) for each prime divisor q of p - 1. The primes q are then proved ... Contributed by: Stan Wagon (Macalester College)