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a(n) = floor(n*(n-1)/13).
1

%I #22 Aug 15 2021 05:09:49

%S 0,0,0,0,0,1,2,3,4,5,6,8,10,12,14,16,18,20,23,26,29,32,35,38,42,46,50,

%T 54,58,62,66,71,76,81,86,91,96,102,108,114,120,126,132,138,145,152,

%U 159,166,173,180,188,196,204,212,220,228,236,245,254,263,272,281,290,300,310

%N a(n) = floor(n*(n-1)/13).

%H Harvey P. Dale, <a href="/A011866/b011866.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_15">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,0,0,0,0,0,0,0,0,1,-2,1).

%F From _R. J. Mathar_, Apr 15 2010: (Start)

%F a(n) = 2*a(n-1) - a(n-2) + a(n-13) - 2*a(n-14) + a(n-15).

%F G.f.: x^5*(1+x^6)/(1+x*(-2+x*(1+x^11*(-1+(2-x)*x)))). (End)

%t Table[Floor[(n(n-1))/13],{n,0,70}] (* or *) LinearRecurrence[{2,-1,0,0,0,0,0,0,0,0,0,0,1,-2,1},{0,0,0,0,0,1,2,3,4,5,6,8,10,12,14},70] (* _Harvey P. Dale_, Nov 10 2019 *)

%K nonn,easy

%O 0,7

%A _N. J. A. Sloane_.