A009836 - OEIS

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A009836

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

0, 2, 8, 368, 16512, 1583104, 199552000, 36445579264, 8620299812864, 2621816292114432, 987354046567284736, 452732308336619290624, 247917555997339251900416, 159904531672039230122491904

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OFFSET

0,2

LINKS

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

FORMULA

a(n) ~ (2*n)! * 8 * tanh(arctan(Pi/2)) / ((4 + Pi^2) * arctan(Pi/2)^(2*n+1)). - Vaclav Kotesovec, Jan 24 2015

MATHEMATICA

Tanh[ x ]*Tan[ Tan[ x ] ] (* Even Part *)

nn = 20; Table[(CoefficientList[Series[Tan[Tan[x]]*Tanh[x], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 24 2015 *)

CROSSREFS

Sequence in context: A220904 A009489 A102597 * A012342 A012348 A219994

Adjacent sequences: A009833 A009834 A009835 * A009837 A009838 A009839

KEYWORD

nonn

AUTHOR

R. H. Hardin

EXTENSIONS

Extended and signs tested Mar 15 1997 by Olivier Gérard.

STATUS

approved