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%I #6 Dec 07 2016 10:23:14
%S 3,9,36,1080,544320,5443200,102643200,392302310400,31384184832000,
%T 1371937222656000,10948059036794880000,1686001091666411520000,
%U 10227171457141309440000,16333304175627528241152000000,457332516917570790752256000000,56839898531183798279208960000000
%N Denominators of coefficients in expansion of 1/(1 + 2 cos(sqrt(x))).
%H Clark Kimberling, <a href="/A279121/b279121.txt">Table of n, a(n) for n = 0..999</a>
%e 1/3 + (1/9)x + (1/36)x^2 + (7/1080)x^3 + ... ; 1/3, 1/9, 1/36, 7/1080, 809/544320, ... = A279120/A279121.
%t z = 30; t = CoefficientList[Series[1/(1 + 2 Cos[Sqrt[x]]), {x, 0, z}], x];
%t Numerator[t]; (* A279120 *)
%t Denominator[t]; (* A279121 *)
%t (1/3) Denominator[t] ; (* A279122 *)
%Y Cf. A279120, A279122.
%K nonn,easy,frac
%O 0,1
%A _Clark Kimberling_, Dec 07 2016
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