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A012152 arctanh(tan(tan(x)))=x+6/3!*x^3+176/5!*x^5+12240/7!*x^7... 0

%I

%S 1,6,176,12240,1561088,318007808,94807748608,38942692972544,

%T 21088169713729536,14558790290337431552,12481351528273319821312,

%U 13009249833253480856289280,16200881782506627598590672896

%N arctanh(tan(tan(x)))=x+6/3!*x^3+176/5!*x^5+12240/7!*x^7...

%F a(n) ~ (2*n)! / (arctan(Pi/4))^(2*n+1). - _Vaclav Kotesovec_, Feb 05 2015

%t nn = 20; Table[(CoefficientList[Series[ArcTanh[Tan[Tan[x]]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* _Vaclav Kotesovec_, Feb 05 2015 *)

%K nonn

%O 0,2

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

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Last modified October 19 03:34 EDT 2019. Contains 328211 sequences. (Running on oeis4.)