A046981 Denominators of Taylor series for exp(x)*cos(x).

1, 1, 1, 3, 6, 30, 1, 630, 2520, 22680, 1, 1247400, 7484400, 97297200, 1, 10216206000, 81729648000, 1389404016000, 1, 237588086736000, 2375880867360000, 49893498214560000, 1, 12623055048283680000, 151476660579404160000, 3786916514485104000000

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• frac
• easy
• nice

Examples

			1+1*x-1/3*x^3-1/6*x^4-1/30*x^5+1/630*x^7+1/2520*x^8+1/22680*x^9-...
		

References

• G. W. Caunt, Infinitesimal Calculus, Oxford Univ. Press, 1914, p. 477.

Links

• T. D. Noe, Table of n, a(n) for n=0..100

Crossrefs

Cf. A046980, A046979, A052277, A007019, A007415, A009775, A092820.

Absolute values are essentially the same as A007452.

Programs

Mathematica

Denominator/@CoefficientList[Series[Exp[x]Cos[x],{x,0,30}],x] (* Harvey P. Dale, Jun 28 2011 *)

Formula

a(4n+2) = 1, a(n) = n!/2^[n/2].