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 A203689 #9 Nov 21 2023 05:33:09
%S A203689 1,5,7400,1515608208000,67968144879431450715389952000,
%T A203689 2618461740951506934762583974466059060153960058218086400000
%N A203689 Vandermonde sequence using x^2 + y^2 applied to (1,2,6,...,n!).
%C A203689 See A093883 for a discussion and guide to related sequences.
%F A203689 a(n) ~ c * n^(2*n^3/3 + n^2/2 - 7*n/6 - 3/4) * (2*Pi)^(n*(n-1)/2) / exp(8*n^3/9 - n^2/4 - 2*n), where c = 0.574053995428296820717722993471497472923951255369819486673614046900594637219... - _Vaclav Kotesovec_, Nov 21 2023
%t A203689 f[j_] := j!; z = 8;
%t A203689 u[n_] := Product[f[j]^2 + f[k]^2, {j, 1, k - 1}]
%t A203689 v[n_] := Product[u[n], {k, 2, n}]
%t A203689 Table[v[n], {n, 1, z}] (* A203689 *)
%t A203689 Table[v[n + 1]/v[n], {n, 1, z}] (* A203690 *)
%K A203689 nonn
%O A203689 1,2
%A A203689 _Clark Kimberling_, Jan 04 2012