A009700 - OEIS

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

A009700

Expansion of tan(tan(x))*x.

0, 2, 16, 432, 23168, 2039040, 265344000, 47773128704, 11359970459648, 3446710775119872, 1299134788619468800, 595445934379289804800, 326113437715996197519360, 210324874581761164037849088

(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 / ((4+Pi^2) * arctan(Pi/2)^(2*n)). - Vaclav Kotesovec, Jan 23 2015

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Tan[Tan[x]]*x , {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jun 08 2014 *)

CROSSREFS

Sequence in context: A282309 A009397 A229023 * A358784 A012030 A012682

Adjacent sequences: A009697 A009698 A009699 * A009701 A009702 A009703

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested Mar 15 1997 by Olivier Gérard.

Previous Mathematica program replaced by Harvey P. Dale, Jun 08 2014

STATUS

approved