A009182 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A009182

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

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

(list; graph; refs; listen; history; text; internal format)

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