A012850 - OEIS

%I #6 Mar 24 2018 10:36:45

%S 1,1,21,765,46473,4371225,594635613,110691178325,27018807872657,

%T 8370279766396593,3208469378545620005,1491108362472114151469,

%U 826269720877603294674201,538334287550086657620232905

%N cosh(sec(x)*arctanh(x))=1+1/2!*x^2+21/4!*x^4+765/6!*x^6+46473/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Cosh[Sec[x]ArcTanh[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Mar 24 2018 *)

%K nonn

%O 0,3

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