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%I #17 Dec 05 2022 06:26:06
%S 1,3,31,686,27036,1688360,154703688,19692332568,3342458334775,
%T 732812082630803,202322386045180686,68898094282978653925,
%U 28443422251718020038049,14029033632468285836567998,8164217197799501761637725983,5545466507405459243366712102466
%N Number of (3*n) X n matrices with nonnegative integer entries and each column sum being 3 up to permutation of rows.
%C Also number of multiset partitions of [1,1,1,2,2,2,...,n,n,n] into nonempty multisets. - _Marko Riedel_, Nov 29 2022
%H Andrew Howroyd, <a href="/A322487/b322487.txt">Table of n, a(n) for n = 0..100</a>
%e a(1) = 3 because up to permutations of rows there are 3 column vectors with sum 3: [1, 1, 1], [2, 1, 0] and [3, 0, 0].
%Y Row n=3 of A219727.
%Y Cf. A165434, A358721.
%K nonn
%O 0,2
%A _Andrew Howroyd_, Dec 11 2018
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