A011864 - OEIS

%I #23 Mar 03 2024 11:54:11

%S 0,0,0,0,1,1,2,3,5,6,8,10,12,14,16,19,21,24,27,31,34,38,42,46,50,54,

%T 59,63,68,73,79,84,90,96,102,108,114,121,127,134,141,149,156,164,172,

%U 180,188,196,205,213,222,231,241,250,260,270,280,290,300,311,321,332,343,355

%N a(n) = floor(n*(n - 1)/11).

%H Harvey P. Dale, <a href="/A011864/b011864.txt">Table of n, a(n) for n = 0..1000</a>

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

%F a(n) = 2*a(n - 1) - a(n - 2) + a(n - 11) - 2*a(n - 12) + a(n - 13).

%F G.f.: x^4*(x^2 - x + 1)*(1 + x^4)/ ((1 - x)^3 * (1 + x + x^2 + x^3 + x^4 + x^5 + x^6 + x^7 + x^8 + x^9 + x^10)). (End)

%t LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 1, 1, 2, 3, 5, 6, 8, 10, 12}, 64] (* _Peter Luschny_, Aug 13 2021 *)

%t Table[Floor[(n(n-1))/11],{n,0,70}] (* _Harvey P. Dale_, Mar 03 2024 *)

%K nonn,easy

%O 0,7

%A _N. J. A. Sloane_.