A011931 a(n) = floor(n*(n-1)*(n-2)*(n-3)/21).

0, 0, 0, 0, 1, 5, 17, 40, 80, 144, 240, 377, 565, 817, 1144, 1560, 2080, 2720, 3497, 4429, 5537, 6840, 8360, 10120, 12144, 14457, 17085, 20057, 23400, 27144, 31320, 35960, 41097, 46765, 53001, 59840, 67320, 75480, 84360, 94001, 104445, 115737, 127920, 141040, 155144, 170280, 186497, 203845, 222377, 242144

Offset

0,6

Links

Table of n, a(n) for n=0..49.

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

Formula

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-7) - 4*a(n-8) + 6*a(n-9) - 4*a(n-10) + a(n-11). - R. J. Mathar, Apr 15 2010

G.f.: x^4 * (1 + x + 3*x^2 - 2*x^3 + 3*x^4 + x^5 + x^6) / ((1 - x)^5 * (1 + x + x^2 + x^3 + x^4 + x^5 + x^6)). - Elmo R. Oliveira, Jul 01 2026

Mathematica

Table[Floor[n (n - 1) (n - 2) (n - 3)/21], {n, 0, 30}] (* Wesley Ivan Hurt, Jun 18 2022 *)

Prog

(Magma) [Floor(n*(n-1)*(n-2)*(n-3)/21) : n in [0..60]]; // Wesley Ivan Hurt, Jul 07 2025

Crossrefs

Sequence in context: A146272 A147035 A146134 * A260981 A078866 A332689

Adjacent sequences: A011928 A011929 A011930 * A011932 A011933 A011934

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved