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Expansion of e.g.f. cos(tan(tan(x))), even terms only.
1

%I #14 Jul 24 2018 21:22:35

%S 1,-1,-15,-513,-31007,-2881089,-376412847,-64825974593,

%T -13951231536191,-3556538162237313,-998391201911168335,

%U -261420586488162589057,-14787500346745601332575,86170769393986400590463039

%N Expansion of e.g.f. cos(tan(tan(x))), even terms only.

%H G. C. Greubel, <a href="/A009068/b009068.txt">Table of n, a(n) for n = 0..223</a>

%t With[{nmax = 60}, CoefficientList[Series[Cos[Tan[Tan[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(tan(tan(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