A012732 - OEIS

%I #7 Nov 28 2016 20:36:33

%S 1,-12,-9968,-77575872,-2494079278848,-227607911866125312,

%T -47454799045677121597440,-19613396255307422099013550080,

%U -14538029942147907114791552602275840

%N cos(arctanh(x)*arctan(x)) = 1-12/4!*x^4-9968/8!*x^8-77575872/12!*x^12...

%t With[{nn=30},Take[CoefficientList[Series[Cos[ArcTanh[x]*ArcTan[x]],{x,0,nn}],x] Range[0,nn-2]!,{1,-1,4}]] (* _Ray Chandler_, Nov 28 2016 *)

%K sign

%O 0,2

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