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cos(tanh(x)*arctan(x))=1-12/4!*x^4+480/6!*x^6-25200/8!*x^8...
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%I #6 May 23 2016 10:48:31

%S 1,0,-12,480,-25200,1789440,-165502656,18976409088,-2521802100480,

%T 337469315481600,-20084172331338752,-21802197506685280256,

%U 22192552544232587431936,-18125174754251391091998720

%N cos(tanh(x)*arctan(x))=1-12/4!*x^4+480/6!*x^6-25200/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Cos[Tanh[x]ArcTan[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, May 23 2016 *)

%K sign

%O 0,3

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