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 A011903 #27 Oct 18 2024 01:19:47
%S A011903 0,0,0,0,1,2,5,10,16,24,34,47,62,81,104,130,160,194,233,276,325,380,
%T A011903 440,506,578,657,742,835,936,1044,1160,1284,1417,1558,1709,1870,2040,
%U A011903 2220,2410,2611,2822,3045,3280
%N A011903 a(n) = floor(n*(n-1)*(n-2)/21).
%H A011903 Vincenzo Librandi, <a href="/A011903/b011903.txt">Table of n, a(n) for n = 0..1000</a>
%H A011903 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1,0,0,0,1,-3,3,-1).
%F A011903 From _R. J. Mathar_, Apr 15 2010: (Start)
%F A011903 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) + a(n-7) - 3*a(n-8) + 3*a(n-9) - a(n-10).
%F A011903 G.f.: x^4*(1-x+2*x^2-x^4+x^5) / ( (1-x)^4*(1+x+x^2+x^3+x^4+x^5+x^6) ). (End)
%t A011903 CoefficientList[Series[x^4*(1-x+2*x^2-x^4+x^5)/((1-x)^3*(1-x^7)), {x,0,60}], x] (* _Vincenzo Librandi_, Jul 07 2012 *)
%t A011903 LinearRecurrence[{3,-3,1,0,0,0,1,-3,3,-1},{0,0,0,0,1,2,5,10,16,24},60] (* _Harvey P. Dale_, May 03 2023 *)
%o A011903 (Magma) [Floor(n*(n-1)*(n-2)/21): n in [0..50]]; // _Vincenzo Librandi_, Jul 07 2012
%o A011903 (SageMath) [2*binomial(n,3)//7 for n in range(61)] # _G. C. Greubel_, Oct 18 2024
%Y A011903 Cf. A011886.
%K A011903 nonn,easy
%O A011903 0,6
%A A011903 _N. J. A. Sloane_