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