A012133 - OEIS

%I #6 Sep 21 2022 14:57:40

%S 1,-1,9,-201,8369,-559601,54852729,-7411089401,1320161221089,

%T -299803443573601,84543945702681449,-28984920596097196201,

%U 11872728882101557841809,-5726623333843769342341201

%N sech(arcsin(tanh(x)))=1-1/2!*x^2+9/4!*x^4-201/6!*x^6+8369/8!*x^8...

%t With[{nn=30},Take[CoefficientList[Series[Sech[ArcSin[Tanh[x]]],{x,0,nn}],x] Range[ 0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Sep 21 2022 *)

%K sign

%O 0,3

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