

A009691


Expansion of tan(tan(sinh(x))) (odd powers only).


0



1, 5, 113, 5781, 520001, 72300997, 14337027825, 3838128112661, 1332896717838849, 582503435362842629, 312774761747765633777, 202388665054249928155157, 155314408487077603685528641
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OFFSET

1,2


LINKS



FORMULA

a(n) ~ (2*n1)! * 8 / ((4+Pi^2) * sqrt(1+arctan(Pi/2)^2) * arcsinh(arctan(Pi/2))^(2*n)).  Vaclav Kotesovec, Jan 23 2015


MATHEMATICA

Tan[ Tan[ Sinh[ x ] ] ] (* Odd Part *)
nn = 20; Table[(CoefficientList[Series[Tan[Tan[Sinh[x]]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Jan 23 2015 *)


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



