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sec(arctanh(x)+arctan(x))=1+4/2!*x^2+80/4!*x^4+4480/6!*x^6...
0

%I #6 Nov 29 2016 10:22:50

%S 1,4,80,4480,462080,77248000,18902835200,6385348403200,

%T 2843287396352000,1614575957622784000,1138477316012441600000,

%U 976037590707833405440000,999765439694232249958400000

%N sec(arctanh(x)+arctan(x))=1+4/2!*x^2+80/4!*x^4+4480/6!*x^6...

%t With[{nn=30},Take[CoefficientList[Series[Sec[ArcTanh[x]+ArcTan[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Ray Chandler_, Nov 29 2016 *)

%K nonn

%O 0,2

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