

A000819


Expansion of cos^2 x /cos 2x.


2



1, 2, 40, 1952, 177280, 25866752, 5535262720, 1633165156352, 635421069967360, 315212388819402752, 194181169538675507200, 145435130631317935357952, 130145345400688287667978240, 137139396592145493713802493952
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OFFSET

0,2


LINKS

R. J. Mathar, Table of n, a(n) for n = 1..200


FORMULA

E.g.f.: cos(x)^2/cos(2x)=1/Q(0)+1/2; Q(k)=1+1/(12*(x^2)/(2*(x^2)(k+1)*(2k+1)/Q(k+1))); (continued fraction).  Sergei N. Gladkovskii, Nov 18 2011


MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Cos[x]^2/Cos[2x], {x, 0, nn}], x] Range[ 0, nn]!, {1, 1, 2}]] (* Harvey P. Dale, Jul 06 2014 *)


CROSSREFS

Essentially the same as A000816.
Second column of array A103905.
Sequence in context: A198248 A163826 A000816 * A060079 A052502 A209289
Adjacent sequences: A000816 A000817 A000818 * A000820 A000821 A000822


KEYWORD

nonn


AUTHOR

N. J. A. Sloane.


STATUS

approved



