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A011940
a(n) = floor(n*(n-1)*(n-2)*(n-3)/30).
2
0, 0, 0, 0, 0, 4, 12, 28, 56, 100, 168, 264, 396, 572, 800, 1092, 1456, 1904, 2448, 3100, 3876, 4788, 5852, 7084, 8500, 10120, 11960, 14040, 16380, 19000, 21924, 25172, 28768, 32736, 37100, 41888, 47124, 52836, 59052, 65800, 73112, 81016, 89544, 98728, 108600, 119196, 130548, 142692, 155664, 169500
OFFSET
0,6
LINKS
FORMULA
a(n) = 4 * A011795(n).
From R. J. Mathar, Apr 15 2010: (Start)
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-5) - 4*a(n-6) + 6*a(n-7) - 4*a(n-8) + a(n-9).
G.f.: 4*x^5*(1-x+x^2) / ((1-x)^5*(1+x+x^2+x^3+x^4) ). (End)
MATHEMATICA
CoefficientList[Series[4*x^5*(1-x+x^2)/((1-x)^4*(1-x^5)), {x, 0, 60}], x] (* Vincenzo Librandi, Jun 19 2012 *)
LinearRecurrence[{4, -6, 4, -1, 1, -4, 6, -4, 1}, {0, 0, 0, 0, 0, 4, 12, 28, 56}, 60] (* Harvey P. Dale, Nov 13 2017 *)
Floor[4*Binomial[Range[0, 60], 4]/5] (* G. C. Greubel, Oct 27 2024 *)
PROG
(Magma) [Floor(n*(n-1)*(n-2)*(n-3)/30): n in [0..60]]; // Vincenzo Librandi, Jun 19 2012
(SageMath) [4*binomial(n, 4)//5 for n in range(61)] # G. C. Greubel, Oct 27 2024
CROSSREFS
Sequence in context: A006000 A161216 A085622 * A223764 A102653 A102650
KEYWORD
nonn,easy,changed
STATUS
approved