A009043 Expansion of cos(sin(x))/cos(x), even terms only.

1, 0, 4, 24, 848, 25792, 1491392, 106879616, 10504954112, 1298259085312, 200164547589120, 37466482286032896, 8382720548500262912, 2208241619066995294208, 676599830605856131694592

Offset

0,3

Links

G. C. Greubel, Table of n, a(n) for n = 0..242

Formula

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

Mathematica

nn = 20; Table[(CoefficientList[Series[Cos[Sin[x]]*Sec[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(sin(x))/cos(x))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jul 23 2018

Crossrefs

Sequence in context: A196866 A326794 A223005 * A024251 A193484 A024252

Adjacent sequences: A009040 A009041 A009042 * A009044 A009045 A009046

Keyword

nonn

Author

R. H. Hardin

Extensions

Extended and signs tested Mar 15 1997 by Olivier Gérard.

Status

approved