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 A212983 #18 Nov 19 2021 12:08:44
%S A212983 1,5,15,33,62,104,162,238,335,455,601,775,980,1218,1492,1804,2157,
%T A212983 2553,2995,3485,4026,4620,5270,5978,6747,7579,8477,9443,10480,11590,
%U A212983 12776,14040,15385,16813,18327,19929,21622,23408,25290,27270,29351
%N A212983 Number of (w,x,y) with all terms in {0,...,n} and w<=x+y and x<=y.
%C A212983 For a guide to related sequences, see A212959.
%H A212983 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2,-2,3,-1).
%F A212983 a(n) = 3*a(n-1) - 2*a(n-2) - 2*a(n-3) + 3*a(n-4) - a(n-5).
%F A212983 G.f.: (1 + 2*x + 2*x^2)/((1 + x)*(1 - x)^4).
%F A212983 From _Ayoub Saber Rguez_, Oct 11 2021: (Start)
%F A212983 a(n) = A212982(n) + A002620(n+2).
%F A212983 a(n) = (10*n^3 + 39*n^2 + 50*n + 24 - 3*(n mod 2))/24. (End)
%t A212983 t = Compile[{{n, _Integer}}, Module[{s = 0},
%t A212983 (Do[If[w <= x + y && x <= y, s = s + 1],
%t A212983 {w, 0, n}, {x, 0, n}, {y, 0, n}]; s)]];
%t A212983 m = Map[t[#] &, Range[0, 60]] (* A212983 *)
%Y A212983 Cf. A002620, A212959, A212982.
%K A212983 nonn,easy
%O A212983 0,2
%A A212983 _Clark Kimberling_, Jun 04 2012