A011904 a(n) = floor( n*(n-1)*(n-2)/22 ).

0, 0, 0, 0, 1, 2, 5, 9, 15, 22, 32, 45, 60, 78, 99, 124, 152, 185, 222, 264, 310, 362, 420, 483, 552, 627, 709, 797, 893, 996, 1107, 1225, 1352, 1488, 1632, 1785, 1947, 2119, 2300, 2492, 2694, 2907, 3130, 3365, 3612, 3870, 4140, 4422, 4717, 5024, 5345, 5679, 6027, 6388, 6764, 7155, 7560, 7980, 8415, 8866, 9332, 9815, 10314, 10830, 11362, 11912, 12480, 13065, 13668

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A011886.

Programs

Magma

[Floor(3*Binomial(n,3)/11): n in [0..80]]; // G. C. Greubel, Oct 18 2024

Mathematica

Table[Floor[(n(n-1)(n-2))/22],{n,0,80}] (* Harvey P. Dale, Sep 30 2019 *)

SageMath

[3*binomial(n,3)//11 for n in range(81)] # G. C. Greubel, Oct 18 2024

Formula

G.f.: x^4*(1-x+2*x^2-x^3+x^4-x^5+2*x^6-x^8+x^9)/((1-x)^4*(1+x+x^2+x^3+x^4+ x^5+x^6+x^7+x^8+x^9+x^10)). - Peter J. C. Moses, Jun 02 2014

Extensions

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