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A011891
a(n) = floor( n*(n-1)*(n-2)/9 ).
2
0, 0, 0, 0, 2, 6, 13, 23, 37, 56, 80, 110, 146, 190, 242, 303, 373, 453, 544, 646, 760, 886, 1026, 1180, 1349, 1533, 1733, 1950, 2184, 2436, 2706, 2996, 3306, 3637, 3989, 4363, 4760, 5180, 5624, 6092, 6586, 7106, 7653, 8227, 8829, 9460, 10120, 10810, 11530
OFFSET
0,5
LINKS
FORMULA
G.f.: x^4*(2-2*x+x^2+x^3-x^4+x^5)/((1+x^3+x^6)*(1-x)^4). [Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009]
Third differences are [-2, 4] repeated. - M. F. Hasler, Sep 15 2009
MATHEMATICA
Table[Floor[(n(n-1)(n-2))/9], {n, 0, 40}] (* or *)
LinearRecurrence[{4, -6, 3, 3, -6, 3, 3, -6, 4, -1}, {0, 0, 0, 0, 2, 6, 13, 23, 37, 56}, 50] (* Harvey P. Dale, Feb 20 2017 *)
PROG
(Magma) [Floor(n*(n-1)*(n-2)/9): n in [0..50]]; // Vincenzo Librandi, Feb 23 2017
(SageMath) [2*binomial(n, 3)//3 for n in range(51)] # G. C. Greubel, Oct 06 2024
CROSSREFS
Cf. A011886.
Sequence in context: A293503 A143689 A180773 * A370880 A184533 A338991
KEYWORD
nonn
STATUS
approved