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%I #10 Feb 01 2022 01:23:58
%S 1,15,1185,230895,83860545,48942778575,41893214676705,
%T 49441928730798255,76946148390480577665,152682246738275154625935,
%U 376229085883258481118811425,1127131459348047116845576437615,4034538627668651235506091915425985
%N Expansion of cos x / cos 4x.
%H T. D. Noe, <a href="/A001728/b001728.txt">Table of n, a(n) for n = 0..50</a>
%t nn = 22; t = Range[0, nn]! CoefficientList[Series[Cos[x]/Cos[4 x], {x, 0, nn}], x]; Take[t, {1, nn, 2}];
%Y Bisection of A000813.
%K nonn
%O 0,2
%A _N. J. A. Sloane_
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