A009701 Expansion of e.g.f. tan(tan(x))/cos(x), odd powers only.

1, 7, 137, 5535, 386481, 41604055, 6390472441, 1326107352879, 357130810766305, 121056393177867303, 50420813008501457897, 25307979564532627724095, 15065045963101006722139793

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..100

Formula

a(n) ~ 4 * (2*n+1)! / (sqrt(4+Pi^2) * (arctan(Pi/2))^(2*n+2)). - Vaclav Kotesovec, Apr 20 2014

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Tan[Tan[x]]/Cos[x], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Aug 25 2013 *)

Crossrefs

Sequence in context: A100520 A221342 A221298 * A120052 A171106 A217504

Adjacent sequences: A009698 A009699 A009700 * A009702 A009703 A009704

Keyword

nonn

Author

R. H. Hardin

Extensions

Extended and signs tested by Olivier Gérard, Mar 15 1997

Prior Mathematica program deleted by Harvey P. Dale, Aug 25 2013

Clarified definition - Joerg Arndt, Feb 09 2014

Status

approved