If p is prime, Mp = 2V -1 is called a Mersenne number. The primes Af4263 and Mmz were discovered by coding the Lucas-Lehmer test for the IBM 7090. These two new primes are the largest prime numbers known; for other large primes see Robinson [4]. The computing was done at the UCLA Computing Facility. This test is described by the following theorem (see Lehmer [1,). Theorem. If Si = á and Sn+i = Sn2 -2 then Mv is prime if and only if Sp-i = 0 (mod Mp).