A012233 - OEIS

%I #6 Nov 28 2016 18:08:29

%S 1,-2,32,-944,64640,-5881600,919673856,-172830523392,48225099218944,

%T -15466881283850240,6745794347282989056,-3302151520495305490432,

%U 2072514460288282576027648,-1438958551527596730993344512

%N arctan(arctan(arctanh(x)))=x-2/3!*x^3+32/5!*x^5-944/7!*x^7+64640/9!*x^9...

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