%I #6 Aug 27 2019 15:30:57
%S 1,0,-12,-120,1680,367680,12095424,-560956032,-447394871040,
%T -8068784621568,-1294533276204032,6639186363172284416,
%U -1043706052752056152064,641443809049086939217920
%N sech(arcsinh(x)*tan(x))=1-12/4!*x^4-120/6!*x^6+1680/8!*x^8...
%t With[{nn=30},Take[CoefficientList[Series[Sech[ArcSinh[x]Tan[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Aug 27 2019 *)
%K sign
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)