A012061 - OEIS

%I #6 Sep 24 2021 17:03:46

%S 1,1,9,201,7921,447281,28121145,230243001,-940995291295,

%T -539358796035359,-280768914546419735,-156059839698555664599,

%U -96215805882840361663151,-66431831409927100446899439

%N sec(sin(arctanh(x)))=1+1/2!*x^2+9/4!*x^4+201/6!*x^6+7921/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Sec[Sin[ArcTanh[x]]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Sep 24 2021 *)

%K sign

%O 0,3

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