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Floor( n*(n-1)/22 ).
1

%I #11 Feb 23 2016 18:36:58

%S 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,

%T 34,36,39,42,45,48,51,54,57,60,63,67,70,74,78,82,86,90,94,98,102,106,

%U 111,115,120,125,130,135,140,145,150,155,160,166,171,177,183,189,195,201,207

%N Floor( n*(n-1)/22 ).

%H <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1).

%F 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) ). [_R. J. Mathar_, Apr 15 2010]

%t 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]

%K nonn,easy

%O 0,9

%A _N. J. A. Sloane_.