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Numbers k such that 2^psi(k) == -1 (mod k) where psi(k) = A001615(k).
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%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