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A012237 arctanh(arctan(arctanh(x)))=x+2/3!*x^3+32/5!*x^5+1168/7!*x^7+80768/9!*x^9... 0
1, 2, 32, 1168, 80768, 8855296, 1420471296, 312821661696, 90619729117184, 33397289918332928, 15260151754256547840, 8466388564521610903552, 5606464118961336397856768, 4368144479139164180218642432 (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)! / (tanh(tan(1)))^(2*n+1). - Vaclav Kotesovec, Feb 05 2015

MATHEMATICA

nn = 20; Table[(CoefficientList[Series[ArcTanh[ArcTan[ArcTanh[x]]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 05 2015 *)

CROSSREFS

Sequence in context: A012198 A012114 A055929 * A012093 A012214 A320419

Adjacent sequences:  A012234 A012235 A012236 * A012238 A012239 A012240

KEYWORD

nonn

AUTHOR

Patrick Demichel (patrick.demichel(AT)hp.com)

STATUS

approved

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Last modified October 22 19:53 EDT 2019. Contains 328319 sequences. (Running on oeis4.)