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tan(arctanh(x)*arctan(x))=2/2!*x^2+448/6!*x^6+2138112/10!*x^10...
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%I #6 Sep 24 2013 14:42:39

%S 2,448,2138112,53551718400,4262315839979520,826978943730607718400,

%T 331594807758028302723317760,245412719115132295441404238233600,

%U 308745457206861968420290988707864903680,620129923454446057412994114512456319793889280

%N tan(arctanh(x)*arctan(x))=2/2!*x^2+448/6!*x^6+2138112/10!*x^10...

%t With[{nn=40},Take[CoefficientList[Series[Tan[ArcTanh[x]ArcTan[x]],{x,0,nn}],x] Range[0,nn-2]!,{3,-1,4}]] (* _Harvey P. Dale_, Sep 24 2013 *)

%K nonn

%O 0,1

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

%E Definition clarified by and more terms from _Harvey P. Dale_, Sep 24 2013