A279121 Denominators of coefficients in expansion of 1/(1 + 2 cos(sqrt(x))).

3, 9, 36, 1080, 544320, 5443200, 102643200, 392302310400, 31384184832000, 1371937222656000, 10948059036794880000, 1686001091666411520000, 10227171457141309440000, 16333304175627528241152000000, 457332516917570790752256000000, 56839898531183798279208960000000

Offset

0,1

Links

Clark Kimberling, Table of n, a(n) for n = 0..999

Example

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.

Mathematica

z = 30; t = CoefficientList[Series[1/(1 + 2 Cos[Sqrt[x]]), {x, 0, z}], x];
Numerator[t];  (* A279120 *)
Denominator[t];  (* A279121 *)
(1/3) Denominator[t] ; (* A279122 *)

Crossrefs

Cf. A279120, A279122.

Sequence in context: A163144 A128094 A135474 * A076964 A034808 A018398

Adjacent sequences: A279118 A279119 A279120 * A279122 A279123 A279124

Keyword

nonn,easy,frac

Author

Clark Kimberling, Dec 07 2016

Status

approved