A012171 arctanh(tan(tanh(x)))=x+2/3!*x^3+16/5!*x^5+496/7!*x^7+24064/9!*x^9...

1, 2, 16, 496, 24064, 1908224, 227958784, 36620830720, 7865201852416, 2142236553248768, 725477781101608960, 298762982193334583296, 146937839959786186080256, 85124605007437662078894080

Offset

0,2

Links

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

Formula

a(n) ~ (2*n)! / (arctanh(Pi/4))^(2*n+1). - Vaclav Kotesovec, Feb 05 2015

Mathematica

With[{nn=30}, Take[CoefficientList[Series[ArcTanh[Tan[Tanh[x]]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Nov 19 2011 *)

Crossrefs

Sequence in context: A306816 A012461 A012458 * A068472 A168402 A168406

Adjacent sequences: A012168 A012169 A012170 * A012172 A012173 A012174

Keyword

nonn

Author

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

Status

approved