A011860 Floor( n(n-1)/7 ).

0, 0, 0, 0, 1, 2, 4, 6, 8, 10, 12, 15, 18, 22, 26, 30, 34, 38, 43, 48, 54, 60, 66, 72, 78, 85, 92, 100, 108, 116, 124, 132, 141, 150, 160, 170, 180, 190, 200, 211, 222, 234, 246, 258, 270, 282, 295, 308, 322, 336, 350, 364, 378, 393, 408, 424, 440, 456, 472, 488, 505

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

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

Formula

a(n) = +2*a(n-1) -a(n-2) +a(n-7) -2*a(n-8) +a(n-9). G.f.: x^4*(x^2+1)/ ((1-x)^3 * (1+x+x^2+x^3+x^4+x^5+x^6)). [R. J. Mathar, Apr 15 2010]