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