A012835 - OEIS

%I #6 Jul 30 2020 20:08:02

%S 1,-1,25,-761,42065,-3898321,521329705,-96017526281,23356125062945,

%T -7240133620964641,2786977252450841785,-1304375789021987253401,

%U 729394652578427432666225,-480281453260247282387992561

%N arctan(sec(x)*tanh(x))=x-1/3!*x^3+25/5!*x^5-761/7!*x^7+42065/9!*x^9...

%t With[{nn=30},Take[CoefficientList[Series[ArcTan[Sec[x]Tanh[x]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Jul 30 2020 *)

%K sign

%O 0,3

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