A011908 a(n) = floor( n*(n-1)*(n-2)/26 ).

0, 0, 0, 0, 0, 2, 4, 8, 12, 19, 27, 38, 50, 66, 84, 105, 129, 156, 188, 223, 263, 306, 355, 408, 467, 530, 600, 675, 756, 843, 936, 1037, 1144, 1259, 1380, 1510, 1647, 1793, 1946, 2109, 2280, 2460, 2649, 2847, 3056, 3274, 3503, 3741, 3991, 4251, 4523, 4805, 5100, 5406, 5724, 6054, 6396, 6752, 7120

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,-3,1,0,0,0,0,0,0,0,0,0,1,-3,3,-1).

Crossrefs

Cf. A011886.

Programs

Magma

[Floor(3*Binomial(n,3)/13): n in [0..75]]; // G. C. Greubel, Oct 18 2024

Mathematica

Floor[3*Binomial[Range[0, 75], 3]/13] (* G. C. Greubel, Oct 18 2024 *)

SageMath

[3*binomial(n,3)//13 for n in range(76)] # G. C. Greubel, Oct 18 2024

Formula

From R. J. Mathar, Apr 15 2010: (Start)

a(n) = +3*a(n-1) -3*a(n-2) +a(n-3) +a(n-13) -3*a(n-14) +3*a(n-15) -a(n-16).

G.f.: x^5*(2-2*x+2*x^2-2*x^3+3*x^4-2*x^5+2*x^6-2*x^7+3*x^8-2*x^9+x^10) / ( (1-x)^3*(1-x^13) ). (End)

Extensions

More terms added by G. C. Greubel, Oct 18 2024