A011913 a(n) = floor(n*(n - 1)*(n - 2)/31).

0, 0, 0, 0, 0, 1, 3, 6, 10, 16, 23, 31, 42, 55, 70, 88, 108, 131, 157, 187, 220, 257, 298, 342, 391, 445, 503, 566, 634, 707, 785, 870, 960, 1056, 1158, 1266, 1381, 1503, 1632, 1768, 1912, 2063, 2221, 2388, 2563, 2746, 2938, 3138, 3347, 3565, 3793, 4030, 4277, 4534, 4800, 5077, 5365, 5663, 5972, 6292, 6623, 6965, 7320, 7686, 8064, 8454, 8856, 9271, 9699, 10140, 10594

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 0..2000
• Index entries for linear recurrences with constant coefficients, signature (3,-3,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-3,3,-1).

Crossrefs

Cf. A011886.

Programs

Magma

[Floor(6*Binomial(n,3)/31): n in [0..80]]; // G. C. Greubel, Oct 19 2024

Mathematica

Floor[6*Binomial[Range[0,80], 3]/31] (* G. C. Greubel, Oct 19 2024 *)

PARI

a(n) = n*(n-1)*(n-2)\31 \\ Jianing Song, Oct 15 2018

SageMath

[6*binomial(n,3)//31 for n in range(81)] # G. C. Greubel, Oct 19 2024

Formula

G.f.: x^5*(1 +x^4 -x^5 +2*x^7 -x^8 +x^10 -x^11 +x^12 +x^14 -x^15 +x^16 -x^18 +2*x^19 -x^21 +x^22 +2*x^26 -2*x^27 +x^28)/((1-x)^3*(1-x^31)). - Peter J. C. Moses, Jun 02 2014

Extensions

More terms added by G. C. Greubel, Oct 19 2024