A011867 a(n) = floor(n*(n-1)/14).

0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21, 24, 27, 30, 33, 36, 39, 42, 46, 50, 54, 58, 62, 66, 70, 75, 80, 85, 90, 95, 100, 105, 111, 117, 123, 129, 135, 141, 147, 154, 161, 168, 175, 182, 189, 196, 204, 212, 220, 228, 236, 244, 252, 261, 270, 279, 288, 297

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..10000
• Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,1,-2,1).

Crossrefs

Cf. A174738, A008725.

Programs

Magma

[Floor(n*(n-1)/14): n in [0..70]]; // Vincenzo Librandi, Aug 29 2011

Mathematica

Table[Floor[n(n - 1)/14], {n, 0, 59}] (* Alonso del Arte, Aug 26 2011 *)
LinearRecurrence[{2,-1,0,0,0,0,1,-2,1},{0,0,0,0,0,1,2,3,4},70] (* Harvey P. Dale, Oct 22 2016 *)

Formula

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

a(n) = 2*a(n-1) - a(n-2) + a(n-7) - 2*a(n-8) + a(n-9).

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