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%I #9 Nov 28 2016 18:13:59
%S 1,2,32,1168,80768,8855296,1420471296,312821661696,90619729117184,
%T 33397289918332928,15260151754256547840,8466388564521610903552,
%U 5606464118961336397856768,4368144479139164180218642432
%N arctanh(arctan(arctanh(x)))=x+2/3!*x^3+32/5!*x^5+1168/7!*x^7+80768/9!*x^9...
%F a(n) ~ (2*n)! / (tanh(tan(1)))^(2*n+1). - _Vaclav Kotesovec_, Feb 05 2015
%t nn = 20; Table[(CoefficientList[Series[ArcTanh[ArcTan[ArcTanh[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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