%I
%S 1,2,4,6,8,12,16,18,20,24,32,36,40,42,48,54,60,64,72,80,84,96,100,108,
%T 120,126,128,136,144,156,160,162,168,180,192,200,216,220,240,252,256,
%U 272,288,294,300,312,320,324,336,342,360,378,384,400,408,420,432,440
%N Numbers n such that 2^n == 4^n (mod n).
%C If k is in the sequence then 2k is also in the sequence, but the converse is not true.
%C Contains A124240 as a subsequence. Their difference is given by A124241.  _T. D. Noe_, May 30 2003
%C Also, integers n such that A007733(n) divides n. Also, integers n such that for every odd prime divisor p of n, A007733(p) = A002326((p1)/2) divides n. Also, integers n such that A000265(n) divides 2^n1.  _Max Alekseyev_, Aug 25 2013
%H T. D. Noe, <a href="/A068563/b068563.txt">Table of n, a(n) for n = 1..1000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CarmichaelFunction.html">Carmichael Function</a>
%t Select[Range[500], PowerMod[2,#,# ] == PowerMod[4,#,# ] & ]
%Y Cf. A002322.
%K easy,nonn
%O 1,2
%A _Benoit Cloitre_, Mar 25 2002
%E Comment and Mathematica program corrected by _T. D. Noe_, Oct 17 2008
