146.—TWO NEW MERSENNE PRIMES. The program described in Notes 131(c) and 138 [MTAC, v. 6, p. 61, 204] has been continued. Two more Mersenne primes , 2 2203  - 1 and 2 2281  - 1, were discovered by the SWAC on October 7 and 9, 1952. The time required for either of the tests is one hour. This makes 17 Mersenne primes, and a corresponding number of perfect numbers, now known. They are 2 n  - 1 for n = 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, and 2281.
D. H. L.