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

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

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

Programs

Magma

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

Mathematica

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

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