%I #21 Sep 08 2022 08:46:23
%S 1,3,4,5,6,8,10,12,384,640,768,896,960,24576,49152,950272,1425408,
%T 1572864,3145728,10485760,19398656,65011712,100663296,110057537,
%U 201326592,220115074,671088640,1879048192
%N Numbers k such that 2^phi(k) == phi(k)^2 (mod k^2).
%C Sequence is infinite, i.e., 3*2^(3*(t-1)-(-1)^t) is a term for all t > 0.
%C Prime terms (5, 110057537, ...) are in A246568 based on case A = +1.
%o (PARI) isok(n) = Mod(2, n^2)^eulerphi(n)==eulerphi(n)^2;
%o (Magma) [1] cat [n: n in [1..10^6] | 2^EulerPhi(n) mod n^2 eq EulerPhi(n)^2]; // _Vincenzo Librandi_, Sep 20 2018
%Y Cf. A077815, A077816, A246568, A292544.
%K nonn,more
%O 1,2
%A _Altug Alkan_, Sep 17 2018