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A295255
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Expansion of e.g.f. 2/(1 + sqrt(1 - 4*x*cos(x))).
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6
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1, 1, 4, 27, 288, 4145, 75360, 1655003, 42628096, 1260274689, 42070233600, 1565308844539, 64237925148672, 2882670856605553, 140430196702035968, 7380867094885024635, 416320345406371921920, 25084955259883686000257, 1608058868442709001895936, 109278344982307590211482971
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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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E.g.f.: 1/(1 - x*cos(x)/(1 - x*cos(x)/(1 - x*cos(x)/(1 - x*cos(x)/(1 - ...))))), a continued fraction.
a(n) ~ sqrt(2 - 2*r*sqrt(16*r^2 - 1)) * n^(n-1) / (exp(n) * r^n), where r = A196605 = 0.2585985822541894903... is the root of the equation r*cos(r) = 1/4. - Vaclav Kotesovec, Nov 18 2017
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MAPLE
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a:=series(2/(1+sqrt(1-4*x*cos(x))), x=0, 21): seq(n!*coeff(a, x, n), n=0..19); # Paolo P. Lava, Mar 27 2019
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MATHEMATICA
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nmax = 19; CoefficientList[Series[2/(1 + Sqrt[1 - 4 x Cos[x]]), {x, 0, nmax}], x] Range[0, nmax]!
nmax = 19; CoefficientList[Series[1/(1 + ContinuedFractionK[-x Cos[x], 1, {k, 1, nmax}]), {x, 0, nmax}], x] Range[0, nmax]!
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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