%I A000117 M1150 N0438
%S A000117 1,2,4,8,18,44,122,362,1162,3914,13648,48734,176906,649532,2405236,8964800,
%T A000117 33588234,126390032,477353376,1808676326,6872485104,26179922024,99957747388,
%U A000117 382443112538,1466024067850,5629516646996,21651955485304,83400061453514
%N A000117 Number of even sequences with period 2n (bisection of A000011).
%D A000117 E. N. Gilbert and J. Riordan, Symmetry types of periodic sequences, Illinois 
               J. Math., 5 (1961), 657-665.
%D A000117 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000117 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%Y A000117 Sequence in context: A088457 A006786 A125809 this_sequence A006771 A113989 
               A126757
%Y A000117 Adjacent sequences: A000114 A000115 A000116 this_sequence A000118 A000119 
               A000120
%K A000117 nonn,easy,nice
%O A000117 0,2
%A A000117 N. J. A. Sloane (njas(AT)research.att.com).
%E A000117 More terms from David W. Wilson (davidwwilson(AT)comcast.net), Jan 13, 
               2000.