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A011919
a(n) = floor(n*(n-1)*(n-2)*(n-3)/9).
1
0, 0, 0, 0, 2, 13, 40, 93, 186, 336, 560, 880, 1320, 1906, 2669, 3640, 4853, 6346, 8160, 10336, 12920, 15960, 19506, 23613, 28336, 33733, 39866, 46800, 54600, 63336, 73080, 83906, 95893, 109120, 123669, 139626, 157080, 176120, 196840, 219336, 243706, 270053, 298480
OFFSET
0,5
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-9) - 4*a(n-10) + 6*a(n-11) - 4*a(n-12) + a(n-13).
G.f.: x^4*(2 + 5*x + 3*x^3 + 4*x^4 + 3*x^5 + 5*x^7 + 2*x^8) / ( (1-x)^5*(1+x+x^2)*(x^6+x^3+1) ). (End)
MATHEMATICA
Table[Floor[n(n-1)(n-2)(n-3)/9], {n, 0, 40}] (* or *) LinearRecurrence[ {4, -6, 4, -1, 0, 0, 0, 0, 1, -4, 6, -4, 1}, {0, 0, 0, 0, 2, 13, 40, 93, 186, 336, 560, 880, 1320}, 40] (* Harvey P. Dale, Jan 01 2019 *)
PROG
(PARI) a(n) = floor(n*(n-1)*(n-2)*(n-3)/9); \\ Jinyuan Wang, Feb 28 2020
CROSSREFS
Sequence in context: A119535 A210849 A216155 * A323684 A264529 A263979
KEYWORD
nonn,easy
EXTENSIONS
More terms from Jinyuan Wang, Feb 28 2020
STATUS
approved