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 A176176 Numbers n such that (2^(n-1) mod n)=(4^(n-1) mod n). 2

%I

%S 1,2,3,4,5,7,8,11,13,16,17,19,23,28,29,31,32,37,41,43,47,53,59,61,64,

%T 67,71,73,79,83,89,97,101,103,107,109,112,113,127,128,131,137,139,149,

%U 151,157,163,167

%N Numbers n such that (2^(n-1) mod n)=(4^(n-1) mod n).

%C Numbers n such that A062173(n)=A062175(n).

%C Question: is the sequence (Powers of 2) UNION (odd primes), the union of A000079 and A005408?

%C The answer to the question is No: 2^(28-1) mod 28 = 4^(28-1) mod 28 = 8. Also, any base-2 Fermat pseudoprime (A001567) is a member of this sequence. - _D. S. McNeil_, Dec 07 2010

%H Harvey P. Dale, <a href="/A176176/b176176.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[200],PowerMod[2,#-1,#]==PowerMod[4,#-1,#]&] (* _Harvey P. Dale_, Nov 10 2011 *)

%Y Cf. A000079, A005408, A062173.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Dec 07 2010

%E Extended by _D. S. McNeil_, Dec 07 2010

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Last modified February 28 09:06 EST 2020. Contains 332323 sequences. (Running on oeis4.)