A009813 Expansion of tanh(tan(x))/cos(x).

1, 3, 17, 147, 3265, 248259, 25402769, 2697740307, 299763466753, 36321927229443, 5149754111041937, 933794260030934547, 223162280662322953153, 65749433548871560459971

Offset

0,2

Links

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

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Tanh[Tan[x]]/Cos[x], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Aug 15 2021 *)

Crossrefs

Sequence in context: A052807 A080253 A234289 * A319946 A213507 A305471

Adjacent sequences: A009810 A009811 A009812 * A009814 A009815 A009816

Keyword

nonn

Author

R. H. Hardin

Extensions

Extended and signs tested Mar 15 1997 by Olivier Gérard.

Prior Mathematica program replaced by Harvey P. Dale, Aug 15 2021

Status

approved