A046981 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,4

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

FORMULA

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

EXAMPLE

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-...

MATHEMATICA

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

CROSSREFS

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

Absolute values are essentially the same as A007452.

Sequence in context: A351069 A369607 A007452 * A065943 A275786 A025555

Adjacent sequences: A046978 A046979 A046980 * A046982 A046983 A046984

KEYWORD

nonn,frac,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved