%I A101921
%S A101921 0,1,4,4,8,9,12,11,16,17,20,20,24,25,28,26,32,33,36,36,40,41,44,43,48,
%T A101921 49,52,52,56,57,60,57,64,65,68,68,72,73,76,75,80,81,84,84,88,89,92,90,
%U A101921 96,97,100,100,104,105,108,107,112,113,116,116,120,121,124,120,128
%N A101921 a(2n) = a(n) + 2n - 1, a(2n+1) = 4n.
%C A101921 Exponent of 2 in tangent numbers A000182. Also, exponent of 2 in the 
               sequences A008775, A009670, A009764, A009798, A012227, A024236, A024277, 
               A024299, A052510.
%F A101921 a(n) = 2[A000265(n)-1] - A007814(n) + 2n[1-(1/2)^A007814(n)].
%F A101921 G.f.: Sum[k>=0, t^2(t^2+4t+1)/(1-t^2)^2, t=x^2^k].
%Y A101921 Equals A007814(A000182(n)).
%Y A101921 Sequence in context: A071339 A146890 A145447 this_sequence A093340 A046558 
               A014687
%Y A101921 Adjacent sequences: A101918 A101919 A101920 this_sequence A101922 A101923 
               A101924
%K A101921 nonn
%O A101921 1,3
%A A101921 Ralf Stephan (ralf(AT)ark.in-berlin.de), Dec 21 2004