%I #8 Sep 15 2023 15:04:45
%S 1,-1,-11,-253,-9015,-362009,2294909,7143505067,2709263596817,
%T 958529947538255,359564035447469189,146418020203030157779,
%U 64393370639942123229401,29924760789755403918019639
%N sech(tan(tan(x))) = 1-1/2!*x^2-11/4!*x^4-253/6!*x^6-9015/8!*x^8 ... .
%t With[{nn=30},Take[CoefficientList[Series[Sech[Tan[Tan[x]]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Sep 15 2023 *)
%K sign
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)