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 A303916 #37 Aug 08 2019 19:56:08
%S A303916 0,0,12,84,324,924,2184,4536,8568,15048,24948,39468,60060,88452,
%T A303916 126672,177072,242352,325584,430236,560196,719796,913836,1147608,
%U A303916 1426920,1758120,2148120,2604420,3135132,3749004,4455444,5264544,6187104,7234656,8419488,9754668
%N A303916 Constant term in the expansion of (Sum_{k=0..n} k*(x^k + x^(-k)))^3.
%H A303916 Seiichi Manyama, <a href="/A303916/b303916.txt">Table of n, a(n) for n = 0..10000</a>
%H A303916 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (6,-15,20,-15,6,-1).
%F A303916 a(n) = (n-1) * n * (n+1) * (n+2) * (2*n+1) / 10.
%t A303916 a[n_] := Coefficient[Expand[Sum[k * (x^k + x^(-k)), {k, 0, n}]^3], x, 0]; Array[a, 30, 0] (* _Amiram Eldar_, Dec 16 2018 *)
%t A303916 Table[((n-1)n(n+1)(n+2)(2n+1))/10,{n,0,50}] (* _Harvey P. Dale_, Jul 01 2019 *)
%o A303916 (PARI) {a(n) = polcoeff((sum(k=0, n, k*(x^k+x^(-k))))^3, 0, x)}
%o A303916 (PARI) {a(n) = (n-1)*n*(n+1)*(n+2)*(2*n+1)/10}
%o A303916 (GAP) List([0..35],n->(n-1)*n*(n+1)*(n+2)*(2*n+1)/10); # _Muniru A Asiru_, Dec 16 2018
%Y A303916 Column 3 of A322549.
%K A303916 nonn,easy
%O A303916 0,3
%A A303916 _Seiichi Manyama_, Dec 16 2018