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arctanh(tan(sinh(x)))=x+5/3!*x^3+121/5!*x^5+7069/7!*x^7+763057/9!*x^9...
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%I #12 Feb 05 2015 12:18:03

%S 1,5,121,7069,763057,132103157,33527321257,11731117858573,

%T 5412661283979361,3184128808387236581,2326120405922560979929,

%U 2066008261961436163683709,2192446490036211173903631121

%N arctanh(tan(sinh(x)))=x+5/3!*x^3+121/5!*x^5+7069/7!*x^7+763057/9!*x^9...

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

%t With[{nn=30},Take[CoefficientList[Series[ArcTanh[Tan[Sinh[x]]],{x,0,nn}], x]Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Mar 17 2012 *)

%K nonn

%O 0,2

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

%E More terms from _N. J. A. Sloane_, Aug 27 2006