A012731 - OEIS

%I #7 Nov 28 2016 20:05:58

%S 2,-32,283392,1121740800,157951397068800,14184297129466920960,

%T 5248874425245870210416640,2544005109030684773416383283200

%N arctan(arctanh(x)*arctan(x))=2/2!*x^2-32/6!*x^6+283392/10!*x^10...

%t With[{nn=30},Take[CoefficientList[Series[ArcTan[ArcTanh[x]*ArcTan[x]],{x,0,nn}],x] Range[0,nn]!,{3,-1,4}]] (* _Ray Chandler_, Nov 28 2016 *)

%K sign

%O 0,1

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