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A009105 Expansion of e.g.f. cos(x)/cos(sinh(x)), even powers only. 1
1, 0, 4, 56, 2192, 128448, 11141824, 1332816512, 210250492160, 42290401757184, 10563624419906560, 3208072210301966336, 1164053448822395604992, 497366043438147538010112, 247165485059674632625438720 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..232

FORMULA

a(n) ~ (2*n)! * 4 * cos(arcsinh(Pi/2)) / (sqrt(4+Pi^2) * arcsinh(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 22 2015

MATHEMATICA

nn = 20; Table[(CoefficientList[Series[Cos[x]*Sec[Sinh[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 22 2015 *)

PROG

(PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x)/cos(sinh(x)))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jul 26 2018

CROSSREFS

Sequence in context: A012983 A012959 A013113 * A168481 A171801 A091797

Adjacent sequences: A009102 A009103 A009104 * A009106 A009107 A009108

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested by Olivier Gérard, Mar 15 1997

STATUS

approved

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Last modified December 9 23:05 EST 2022. Contains 358710 sequences. (Running on oeis4.)