A011928 a(n) = floor(n(n-1)(n-2)(n-3)/18).

0, 0, 0, 0, 1, 6, 20, 46, 93, 168, 280, 440, 660, 953, 1334, 1820, 2426, 3173, 4080, 5168, 6460, 7980, 9753, 11806, 14168, 16866, 19933, 23400, 27300, 31668, 36540, 41953, 47946, 54560, 61834, 69813, 78540, 88060, 98420, 109668, 121853, 135026, 149240

Offset

0,6

Links

Table of n, a(n) for n=0..42.

Index entries for linear recurrences with constant coefficients, signature (4, -6, 4, -1, 0, 0, 0, 0, 1, -4, 6, -4, 1).

Formula

From Chai Wah Wu, Aug 02 2020: (Start)

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-9) - 4*a(n-10) + 6*a(n-11) - 4*a(n-12) + a(n-13) for n > 12.

G.f.: x^4*(-x^8 - 2*x^7 - 2*x^6 + 2*x^5 - 6*x^4 + 2*x^3 - 2*x^2 - 2*x - 1)/((x - 1)^5*(x^2 + x + 1)*(x^6 + x^3 + 1)). (End)

Mathematica

Table[Floor[n(n - 1)(n - 2)(n - 3)/18], {n, 0, 50}] (* Stefan Steinerberger, Apr 25 2006 *)

Prog

(PARI) a(n)=n*(n-1)*(n-2)*(n-3)\18 \\ Charles R Greathouse IV, Oct 18 2022

Crossrefs

Sequence in context: A048969 A353692 A005564 * A055455 A203552 A331754

Adjacent sequences: A011925 A011926 A011927 * A011929 A011930 A011931

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Stefan Steinerberger, Apr 25 2006

Status

approved