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 A306206 #16 Jan 30 2019 06:21:00
%S A306206 1,2,13,3445,127028721,1249195963773451,5343245431687763366112193,
%T A306206 14729376926426500067331714992293420777,
%U A306206 36332859343341728199556523379140726537646663631786369
%N A306206 a(n) = Sum_{k=0..n} (n^2)!/((n^2-n*k)!*n!^k).
%H A306206 Seiichi Manyama, <a href="/A306206/b306206.txt">Table of n, a(n) for n = 0..26</a>
%F A306206 From _Vaclav Kotesovec_, Jan 29 2019: (Start)
%F A306206 a(n) ~ 2 * (n^2)! / (n!)^n.
%F A306206 a(n) ~ n^(n^2 - n/2 + 1) / (exp(1/12) * 2^((n-3)/2) * Pi^((n-1)/2)). (End)
%o A306206 (PARI) {a(n) = sum(k=0, n, (n^2)!/((n^2-n*k)!*n!^k))}
%Y A306206 Cf. A206849, A227403, A306207.
%K A306206 nonn
%O A306206 0,2
%A A306206 _Seiichi Manyama_, Jan 29 2019