A279110 Denominators of coefficients in expansion of 2/(1 + cos(sqrt(x))).

1, 4, 24, 2880, 40320, 7257600, 479001600, 697426329600, 20922789888000, 12804747411456000, 2432902008176640000, 264470759477084160000, 620448401733239439360000, 806582922253211271168000000, 304888344611713860501504000000, 4244045756995056938180935680000000

Offset: 0

Author

Clark Kimberling, Dec 07 2016

Keywords

• nonn
• easy
• frac

Examples

			1/1 + (1/4)x + (1/24)x^2 + (17/2880)x^3 + ... ; 1/1, 1/4, 1/24, 17/2880, 31/40320, ... = |A089171|/A279110.
		

Links

• Clark Kimberling, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A089171, A279109.

Programs

Mathematica

z = 26; t = CoefficientList[Series[2/(1 + Cos[Sqrt[x]]), {x, 0, z}], x];
Numerator[t]   (* A089171, unsigned *)
Denominator[t] (* A279110 *)

Formula

2*A279009.