This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A011864 #25 Jul 08 2025 02:41:05
%S A011864 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 A011864 59,63,68,73,79,84,90,96,102,108,114,121,127,134,141,149,156,164,172,
%U A011864 180,188,196,205,213,222,231,241,250,260,270,280,290,300,311,321,332,343,355
%N A011864 a(n) = floor(n*(n - 1)/11).
%H A011864 Harvey P. Dale, <a href="/A011864/b011864.txt">Table of n, a(n) for n = 0..1000</a>
%H A011864 <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 A011864 From _R. J. Mathar_, Apr 15 2010: (Start)
%F A011864 a(n) = 2*a(n - 1) - a(n - 2) + a(n - 11) - 2*a(n - 12) + a(n - 13).
%F A011864 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 A011864 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 A011864 Table[Floor[(n(n-1))/11],{n,0,70}] (* _Harvey P. Dale_, Mar 03 2024 *)
%K A011864 nonn,easy
%O A011864 0,7
%A A011864 _N. J. A. Sloane_