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 A011875 #16 Apr 18 2025 09:53:45
%S A011875 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 A011875 34,36,39,42,45,48,51,54,57,60,63,67,70,74,78,82,86,90,94,98,102,106,
%U A011875 111,115,120,125,130,135,140,145,150,155,160,166,171,177,183,189,195,201,207
%N A011875 a(n) = floor(n*(n-1)/22).
%H A011875 <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 A011875 From _R. J. Mathar_, Apr 15 2010: (Start)
%F A011875 a(n) = +2*a(n-1) -a(n-2) +a(n-11) -2*a(n-12) +a(n-13).
%F A011875 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)). (End)
%t A011875 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 A011875 nonn,easy
%O A011875 0,9
%A A011875 _N. J. A. Sloane_