A Cunningham number is a binomial number of the form C^±(b, n) congruent b^n ± 1 with b>1 and n positive integers. Bases b^k which are themselves powers need not be considered since they correspond to (b^k)^n ± 1 = b^(k n) ± 1. Prime numbers of the form C^±(b, n) are very rare. A necessary (but not sufficient) condition for C^+(2, n) = 2^n + 1 to be prime is that n be of the form n = 2^m. Numbers of the form F_m = C^+(2, 2^m) = 2^(2^m) + 1 are called Fermat numbers, and the only known primes occur for C^+(2, 1) = 3, C^+(2, 2) = 5, C^+(2, 4) = 17, C^+(2, 8) = 257, and C^+(2, 16) = 65537 (i.e., m = 0, 1, 2, 3, 4). The only other primes C^+(b, n) for nontrivial b<=11 and 2<=n<=1000 are C^+(6, 2) = 37, C^+(6, 4) = 1297, and C^+(10, 2) = 101.
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