A009723 Expansion of tan(tanh(x)/cos(x)).

1, 3, 57, 1995, 128881, 12775059, 1796958633, 342118793307, 84276974508769, 26141579246291235, 9956883572644073241, 4570240365824839488747, 2487549038143714062879313, 1584207614996350912703688627

Offset

0,2

Links

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

Formula

a(n) ~ c * d^n * n^(2*n + 3/2), where d = 0.491131788453837761770391039276... and c = 3.6558020994214430118438069889... - Vaclav Kotesovec, Nov 27 2024

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Tan[Tanh[x]/Cos[x]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Dec 15 2014 *)

Crossrefs

Sequence in context: A053774 A254570 A308404 * A069992 A012196 A012090

Adjacent sequences: A009720 A009721 A009722 * A009724 A009725 A009726

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, Dec 15 2014

Status

approved