%I #11 Jun 27 2024 08:43:03
%S 1,4,8,16,28,32,64,112,128,256,341,448,496,512,561,645,1016,1024,1105,
%T 1288,1387,1729,1792,1905,2044,2047,2048,2416,2465,2701,2821,3277,
%U 4033,4096,4369,4371,4672,4681,4984,5461,6601,7168,7936,7957,8128,8192,8321,8481,8911
%N Nonprimes k such that 2^(k-1) == 4^(k-1) (mod k).
%C All powers of two are present.
%t fQ[n_] := !PrimeQ@ n && PowerMod[2, n - 1, n] == PowerMod[4, n - 1, n]; Select[ Range@ 10000, fQ]
%Y Cf. A062173, A062175, A176176.
%K nonn
%O 1,2
%A _Juri-Stepan Gerasimov_, Dec 07 2010
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