A011875 a(n) = floor(n*(n-1)/22).

0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 34, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 67, 70, 74, 78, 82, 86, 90, 94, 98, 102, 106, 111, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 166, 171, 177, 183, 189, 195, 201, 207

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

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

Programs

Mathematica

Table[Floor[(n(n-1))/22],{n,0,70}] (* or *) LinearRecurrence[{2,-1,0,0,0,0,0,0,0,0,1,-2,1},{0,0,0,0,0,0,1,1,2,3,4,5,6},70]

Formula

From R. J. Mathar, Apr 15 2010: (Start)

a(n) = +2*a(n-1) -a(n-2) +a(n-11) -2*a(n-12) +a(n-13).

G.f.: x^6*(x^2 - x + 1)/((1 - x)^3*(1 + x^10 + x^9 + x^8 + x^7 + x^6 + x^5 + x^4 + x^3 + x^2 + x)). (End)