This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A338931 #7 Dec 18 2020 13:50:26 %S A338931 2,2,2,2,2,54,162,8310407949893763072,46438023168,65229815808, %T A338931 396718580736,629856,152461794335880672662217818112 %N A338931 Least b such that b^(2^n) + 1 is an odd Pierpont prime (A005109). %C A338931 Every term is even (A005843) and 3-smooth (A003586). %C A338931 For n = 0, 1, 2, 3, 4, 7, 8, 9, 12, ..., the corresponding number b^(2^n) + 1 is also a Proth prime (A080076), while for n = 5, 6, 10, 11, ..., it is a non-Proth. %C A338931 The form b^(2^n) + 1 is called a generalized Fermat number. %e A338931 a(7) corresponds to prime 8310407949893763072^128 + 1 = (2^47*3^10)^128 + 1. %Y A338931 Cf. A005109, A056993, A334053. %K A338931 nonn,hard,more %O A338931 0,1 %A A338931 _Jeppe Stig Nielsen_, Nov 16 2020