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 A011867 #35 Sep 08 2022 08:44:37
%S A011867 0,0,0,0,0,1,2,3,4,5,6,7,9,11,13,15,17,19,21,24,27,30,33,36,39,42,46,
%T A011867 50,54,58,62,66,70,75,80,85,90,95,100,105,111,117,123,129,135,141,147,
%U A011867 154,161,168,175,182,189,196,204,212,220,228,236,244,252,261,270,279,288,297
%N A011867 a(n) = floor(n*(n-1)/14).
%H A011867 Vincenzo Librandi, <a href="/A011867/b011867.txt">Table of n, a(n) for n = 0..10000</a>
%H A011867 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,0,0,1,-2,1).
%F A011867 From _R. J. Mathar_, Apr 15 2010: (Start)
%F A011867 a(n) = 2*a(n-1) - a(n-2) + a(n-7) - 2*a(n-8) + a(n-9).
%F A011867 G.f.: x^5 / ((1-x)^3*(x^6+x^5+x^4+x^3+x^2+x+1) ). (End)
%t A011867 Table[Floor[n(n - 1)/14], {n, 0, 59}] (* _Alonso del Arte_, Aug 26 2011 *)
%t A011867 LinearRecurrence[{2,-1,0,0,0,0,1,-2,1},{0,0,0,0,0,1,2,3,4},70] (* _Harvey P. Dale_, Oct 22 2016 *)
%o A011867 (Magma) [Floor(n*(n-1)/14): n in [0..70]]; // _Vincenzo Librandi_, Aug 29 2011
%Y A011867 Cf. A174738, A008725.
%K A011867 nonn,easy
%O A011867 0,7
%A A011867 _N. J. A. Sloane_