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tanh(arctan(arctanh(x)))=x-2/3!*x^3+24/5!*x^5-496/7!*x^7+24192/9!*x^9...
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%I #6 Nov 28 2016 18:12:25

%S 1,-2,24,-496,24192,-1246464,150408192,-12132673536,3380973895680,

%T -253363927449600,217523969745223680,4682388187242823680,

%U 35388810383588767825920,8821171867345211810119680

%N tanh(arctan(arctanh(x)))=x-2/3!*x^3+24/5!*x^5-496/7!*x^7+24192/9!*x^9...

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

%K sign

%O 0,2

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