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A011862
a(n) = floor(n*(n-1)/9).
1
0, 0, 0, 0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 17, 20, 23, 26, 30, 34, 38, 42, 46, 51, 56, 61, 66, 72, 78, 84, 90, 96, 103, 110, 117, 124, 132, 140, 148, 156, 164, 173, 182, 191, 200, 210, 220, 230, 240, 250, 261, 272, 283, 294, 306, 318, 330, 342, 354, 367, 380, 393, 406, 420
OFFSET
0,6
FORMULA
From R. J. Mathar, Apr 15 2010: (Start)
G.f.: x^4*(1 + x^4)/ ((1 - x)^3*(1 + x + x^2)*(1 + x^3 + x^6)).
a(n) = 2*a(n-1) - a(n-2) + a(n-9) - 2*a(n-10) + a(n-11). (End)
MATHEMATICA
Table[Floor[(n(n-1))/9], {n, 0, 70}] (* or *) LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 1, 2, 3, 4, 6, 8, 10}, 70] (* Harvey P. Dale, Oct 01 2017 *)
CROSSREFS
Sequence in context: A097602 A347625 A126794 * A122957 A078769 A064375
KEYWORD
nonn,easy
AUTHOR
STATUS
approved