A011940 a(n) = floor(n(n-1)(n-2)(n-3)/30).

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

Offset

0,6

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (4, -6, 4, -1, 1, -4, 6, -4, 1).

Formula

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*(x^2-x+1) / ((1-x)^5*(x^4+x^3+x^2+x+1) ). (End)

Mathematica

CoefficientList[Series[4*x^5*(x^2-x+1)/((1-x)^5*(x^4+x^3+x^2+x+1)), {x, 0, 50}], 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}, 40] (* Harvey P. Dale, Nov 13 2017 *)

Prog

(Magma) [Floor( n*(n-1)*(n-2)*(n-3)/30): n in [0..40]]; // Vincenzo Librandi, Jun 19 2012

Crossrefs

Equals 4 * A011795.

Sequence in context: A006000 A161216 A085622 * A223764 A102653 A102650

Adjacent sequences: A011937 A011938 A011939 * A011941 A011942 A011943

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved