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.