Cunningham Number
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.