%I #11 Aug 11 2021 08:18:20

%S 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,

%T 92,100,108,116,124,132,141,150,160,170,180,190,200,211,222,234,246,

%U 258,270,282,295,308,322,336,350,364,378,393,408,424,440,456,472,488,505

%N Floor( n(n-1)/7 ).

%H <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,0,0,1,-2,1).

%F 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]

%K nonn,easy

%O 0,6

%A _N. J. A. Sloane_.