%I #6 Apr 19 2019 09:03:14
%S 1,0,-12,480,-18480,176640,149396544,-38742692352,6743113079040,
%T -363222941859840,-455485254371044352,322516524038804660224,
%U -135316725169663246512128,19655917963465137568481280
%N sech(tanh(x)*arctan(x))=1-12/4!*x^4+480/6!*x^6-18480/8!*x^8...
%t With[{nn=30},Take[CoefficientList[Series[Sech[Tanh[x]ArcTan[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Apr 19 2019 *)
%K sign
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)