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A012016 arctanh(sin(tan(x)))=x+3/3!*x^3+41/5!*x^5+1299/7!*x^7+74609/9!*x^9... 1
1, 3, 41, 1299, 74609, 6787811, 898506649, 163241051315, 39007280136801, 11866656488375747, 4479287777805494665, 2054673461380880189779, 1125793481954983195433681, 726247496033154181534638755 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 5 00:43 EDT 2020. Contains 333238 sequences. (Running on oeis4.)