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Expansion of e.g.f. cos(sinh(x)/cos(x)), even powers only.
1

%I #14 Jul 24 2018 21:22:15

%S 1,-1,-15,-297,-6783,-70609,18558705,4027228359,727421677185,

%T 134584692783455,26232888936219249,5245335359878123191,

%U 971782758809341914369,96545317222649153850767

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

%H G. C. Greubel, <a href="/A009064/b009064.txt">Table of n, a(n) for n = 0..239</a>

%t With[{nmax = 60}, CoefficientList[Series[Cos[Sinh[x]/Cos[x]], {x, 0, nmax}], x]*Range[0, nmax]!][[1 ;; -1 ;; 2]] (* _G. C. Greubel_, Jul 24 2018 *)

%o (PARI) x='x+O('x^60); v=Vec(serlaplace(cos(sinh(x)/cos(x)))); vector(#v\2,n,v[2*n-1]) \\ _G. C. Greubel_, Jul 24 2018

%K sign

%O 0,3

%A _R. H. Hardin_

%E Extended with signs by _Olivier GĂ©rard_, Mar 15 1997