A009089 - OEIS

%I #20 Jul 25 2018 06:15:38

%S 1,0,8,-56,3968,-133248,13993088,-1139191808,178943504384,

%T -26439024316416,5943319707680768,-1368130407134953472,

%U 421233393478948782080,-137934416762714295631872,56032481949750675250085888

%N Expansion of e.g.f. cos(tanh(x))/cos(x), even powers only.

%H G. C. Greubel, <a href="/A009089/b009089.txt">Table of n, a(n) for n = 0..239</a>

%p seq(coeff(series(factorial(n)*cos(tanh(x))/cos(x), x,n+1),x,n),n=0..30,2); # _Muniru A Asiru_, Jul 25 2018

%t With[{nn=30},Take[CoefficientList[Series[Cos[Tanh[x]]/Cos[x],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Jul 14 2018 *)

%o (PARI) x='x+O('x^50); v=Vec(serlaplace(cos(tanh(x))/cos(x))); vector(#v\2,n,v[2*n-1]) \\ _G. C. Greubel_, Jul 25 2018

%K sign

%O 0,3

%A _R. H. Hardin_

%E Extended with signs by _Olivier Gérard_, Mar 15 1997

%E Prior Mathematica program replaced by _Harvey P. Dale_, Jul 14 2018