A012757 tan(arctanh(x)^2) = 2/2!*x^2 + 16/4!*x^4 + 608/6!*x^6 + 43776/8!*x^8 + ...

0, 2, 16, 608, 43776, 5248512, 937297920, 232869949440, 76704079872000, 32321764442112000, 16950418888812134400, 10823130351189900656640, 8265103101463254238494720, 7437225349735123409814159360

Offset

0,2

Links

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

Formula

a(n) ~ 2^(3/2) * (2*n)! / (sqrt(Pi) * sinh(sqrt(2*Pi)) * (tanh(sqrt(Pi/2)))^(2*n)). - Vaclav Kotesovec, Feb 06 2015

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Tan[ArcTanh[x]^2], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Mar 31 2013 *)

Crossrefs

Sequence in context: A013177 A060279 A369674 * A012464 A277036 A289202

Adjacent sequences: A012754 A012755 A012756 * A012758 A012759 A012760

Keyword

nonn

Author

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

Extensions

Definition clarified by Harvey P. Dale, Mar 31 2013

Status

approved