A012209 arctanh(arctan(arctan(x)))=x-2/3!*x^3+32/5!*x^5-1392/7!*x^7+118400/9!*x^9...

1, -2, 32, -1392, 118400, -16678144, 3517084672, -1037502889984, 407811782836224, -205957880207835136, 129921324821854289920, -100089923129501690626048, 92456928301505596639674368

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