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sech(tanh(x)*arctan(x))=1-12/4!*x^4+480/6!*x^6-18480/8!*x^8...
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%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)