A012016 arctanh(sin(tan(x)))=x+3/3!*x^3+41/5!*x^5+1299/7!*x^7+74609/9!*x^9...

1, 3, 41, 1299, 74609, 6787811, 898506649, 163241051315, 39007280136801, 11866656488375747, 4479287777805494665, 2054673461380880189779, 1125793481954983195433681, 726247496033154181534638755

Offset

0,2

Links

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

Formula

a(n) ~ 2 * (2*n)! / (arctan(Pi/2))^(2*n+1). - Vaclav Kotesovec, Oct 24 2013

Mathematica

Table[n!*SeriesCoefficient[ArcTanh[Sin[Tan[x]]], {x, 0, n}] , {n, 1, 40, 2}] (* Vaclav Kotesovec, Oct 24 2013 *)
With[{nn=30}, Take[CoefficientList[Series[ArcTanh[Sin[Tan[x]]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, Oct 09 2018 *)

Crossrefs

Bisection of A009329.

Sequence in context: A012225 A012129 A012035 * A207993 A187540 A012104

Adjacent sequences: A012013 A012014 A012015 * A012017 A012018 A012019

Keyword

nonn

Author

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

Status

approved