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A000819 Expansion of cos^2 x /cos 2x. 2
1, 2, 40, 1952, 177280, 25866752, 5535262720, 1633165156352, 635421069967360, 315212388819402752, 194181169538675507200, 145435130631317935357952, 130145345400688287667978240, 137139396592145493713802493952 (list; graph; refs; listen; history; text; internal format)
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/(1-2*(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

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Last modified December 22 09:44 EST 2014. Contains 252339 sequences.