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A012209 arctanh(arctan(arctan(x)))=x-2/3!*x^3+32/5!*x^5-1392/7!*x^7+118400/9!*x^9... 0
1, -2, 32, -1392, 118400, -16678144, 3517084672, -1037502889984, 407811782836224, -205957880207835136, 129921324821854289920, -100089923129501690626048, 92456928301505596639674368 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..12.

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[ArcTanh[ArcTan[ArcTan[x]]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Ray Chandler, Nov 28 2016 *)

CROSSREFS

Sequence in context: A012140 A268557 A281183 * A295418 A172286 A129348

Adjacent sequences:  A012206 A012207 A012208 * A012210 A012211 A012212

KEYWORD

sign

AUTHOR

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

STATUS

approved

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Last modified January 17 18:42 EST 2019. Contains 319251 sequences. (Running on oeis4.)