%I #25 Oct 27 2023 21:10:53
%S 1,1,1,-23,-415,849,421089,16027897,-602344127,-137830187103,
%T -6375572516543,1282077224074761,294398207479497377,
%U 6767832711454751473,-10535904130516747834591,-2468712006908963695579879,172926818125145929773139073
%N Expansion of e.g.f.: 1/cos(sin(x)) (even-indexed coefficients only).
%H Alois P. Heinz, <a href="/A009008/b009008.txt">Table of n, a(n) for n = 0..100</a> (first 51 terms from Vincenzo Librandi)
%t f[x_] := Sec@Sin[x]; Table[Derivative[2*n][f][0], {n, 0, 16}] (* _Arkadiusz Wesolowski_, Aug 18 2012 *)
%t With[{nmax = 50}, CoefficientList[Series[1/(Cos[Sin[x]]), {x, 0, nmax}], x]*Range[0, nmax]!][[1 ;; -1 ;; 2]] (* _G. C. Greubel_, Jul 21 2018 *)
%o (PARI) x='x+O('x^50); v=Vec(serlaplace(1/cos(sin(x)))); vector(#v\2,n,v[2*n-1]) \\ _G. C. Greubel_, Jul 21 2018
%K sign
%O 0,4
%A _R. H. Hardin_, _Simon Plouffe_
%E a(16) from _Arkadiusz Wesolowski_, Aug 18 2012
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