A012228 - OEIS

%I #6 Nov 28 2016 18:01:33

%S 1,-2,24,-944,77952,-10623744,2145104896,-602082207744,

%T 224357319278592,-107165894175948800,63836869263529082880,

%U -46390243522547859062784,40392288941602607862906880

%N arctanh(arctan(tanh(x)))=x-2/3!*x^3+24/5!*x^5-944/7!*x^7+77952/9!*x^9...

%t With[{nn=30},Take[CoefficientList[Series[ArcTanh[ArcTan[Tanh[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)