A015921 - OEIS

%I #33 Sep 22 2016 20:15:27

%S 1,2,4,6,10,12,14,22,26,30,34,38,46,58,62,74,82,86,94,106,118,122,132,

%T 134,142,146,158,166,170,178,182,194,202,206,214,218,226,254,262,274,

%U 278,298,302,314,326,334,346,358,362,372,382,386,394,398,422,446

%N Positive integers n such that 2^n == 4 (mod n).

%C Odd terms are given by A173572.

%C For all m, 2^A050259(m)-1 belongs to this sequence.

%H T. D. Noe, <a href="/A015921/b015921.txt">Table of n, a(n) for n = 1..1000</a>

%H OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a>

%t Select[Range[500], PowerMod[2, #, #] == 4 &] (* _Alonso del Arte_, Jul 07 2011 *)

%Y Contains A050990 as a subsequence.

%Y Cf. A015910, A173572.

%K nonn

%O 1,2

%A _Robert G. Wilson v_

%E Edited and terms 1,2,4 prepended by _Max Alekseyev_, Jul 29 2011