A011862 a(n) = floor(n*(n-1)/9).

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

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,0,0,1,-2,1).

Programs

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 *)

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)