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A009009
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Expansion of e.g.f.: 1/cos(sinh(x)) (even-indexed coefficients only).
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5
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1, 1, 9, 177, 6545, 387649, 33646041, 4025701617, 635120351777, 127753094128897, 31911422805749673, 9691219439564235441, 3516474983468155702193, 1502487398886128051614273, 746659439867912626958616441, 427003792367575880943003380721
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) ~ (2*n)! * 4 / (sqrt(4+Pi^2) * (log((Pi+sqrt(4+Pi^2))/2))^(2*n+1)). - Vaclav Kotesovec, Jan 22 2015
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MATHEMATICA
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f[x_] := Sec@Sinh[x]; Table[Derivative[2*n][f][0], {n, 0, 15}] (* Arkadiusz Wesolowski, Aug 18 2012 *)
With[{nn=30}, Take[CoefficientList[Series[1/Cos[Sinh[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Oct 09 2012 *)
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PROG
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(PARI) x='x+O('x^50); v=Vec(serlaplace(1/cos(sinh(x)))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jul 21 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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