A009182 Expansion of cosh(x)/cos(tan(x)).

1, 2, 20, 608, 34320, 3084640, 405224896, 73292662784, 17468683774208, 5306511481924096, 2001393333656871936, 917626310129679884288, 502654675782900203720704, 324215069803278031144280064

Offset

0,2

Links

Table of n, a(n) for n=0..13.

Formula

a(n) ~ (2*n)! * 8 * cosh(arctan(Pi/2)) / ((4+Pi^2) * arctan(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 22 2015

Mathematica

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

Crossrefs

Sequence in context: A275779 A292415 A197743 * A015207 A054941 A012495

Adjacent sequences: A009179 A009180 A009181 * A009183 A009184 A009185

Keyword

nonn

Author

R. H. Hardin

Extensions

Extended and signs tested Mar 15 1997 by Olivier Gérard.

Status

approved