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