OFFSET
1,1
COMMENTS
See A093883 for a discussion and guide to related sequences.
FORMULA
From Vaclav Kotesovec, Nov 21 2023: (Start)
a(n) ~ (n+1)!^(2*n).
a(n) ~ (2*Pi)^n * n^(2*n^2 + 3*n) / exp(2*n^2 - 13/6). (End)
MATHEMATICA
f[j_] := j!; z = 8;
u[n_] := Product[f[j]^2 + f[j] f[k] + f[k]^2,
{j, 1, k - 1}]
v[n_] := Product[u[n], {k, 2, n}]
Table[v[n], {n, 1, z}] (* A203685 *)
Table[v[n + 1]/v[n], {n, 1, z}] (* A203686 *)
Table[Product[k!^2 + k!*(n+1)! + (n+1)!^2, {k, 1, n}], {n, 1, 10}] (* Vaclav Kotesovec, Nov 21 2023 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jan 04 2012
EXTENSIONS
Definition corrected by Georg Fischer, Nov 25 2021
STATUS
approved