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 A291164 #14 Jul 23 2021 02:08:21 %S A291164 1,5,25,125,625,3125,4097,7361,15625,69649,78125,85073,125137,390625, %T A291164 658529,987377,1184033,1953125,2127329,2358529,3187313,3999137, %U A291164 9765625,11194993,16777217,16785409,20128561,20502593,30030769,36164593,40094993,48828125,50281793 %N A291164 Numbers k such that 2^psi(k) == -1 (mod k) where psi(k) = A001615(k). %e A291164 7361 is a term because 7361 = 17*433 divides 2^psi(7361) + 1 = 2^(18*434) + 1. %o A291164 (PARI) a001615(n) = n*sumdivmult(n, d, issquarefree(d)/d); %o A291164 is(n) = Mod(2,n)^a001615(n)==-1; %Y A291164 Cf. A001615, A276238. %K A291164 nonn %O A291164 1,2 %A A291164 _Altug Alkan_, Aug 19 2017