A009813 - OEIS

%I #10 Aug 15 2021 16:20:20

%S 1,3,17,147,3265,248259,25402769,2697740307,299763466753,

%T 36321927229443,5149754111041937,933794260030934547,

%U 223162280662322953153,65749433548871560459971

%N Expansion of tanh(tan(x))/cos(x).

%t With[{nn=30},Take[CoefficientList[Series[Tanh[Tan[x]]/Cos[x],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Aug 15 2021 *)

%K nonn

%O 0,2

%A _R. H. Hardin_

%E Extended and signs tested Mar 15 1997 by _Olivier Gérard_.

%E Prior Mathematica program replaced by _Harvey P. Dale_, Aug 15 2021