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 A321732 #10 Apr 03 2024 05:14:05
%S A321732 1,1,3,11,53,317,2293,19435,188851,2068417,25203807,338117445,
%T A321732 4951449055,78589443061,1343810727205,24626270763109,481489261372381,
%U A321732 10004230113283129,220125503239710879,5113204953106107087,125037079246130168973
%N A321732 Number of nonnegative integer square matrices with sum of entries equal to n, no zero rows or columns, and the same row sums as column sums.
%H A321732 Ludovic Schwob, <a href="/A321732/b321732.txt">Table of n, a(n) for n = 0..30</a>
%e A321732 The a(3) = 11 matrices:
%e A321732 [3]
%e A321732 .
%e A321732 [2 0] [1 1] [1 0] [0 1]
%e A321732 [0 1] [1 0] [0 2] [1 1]
%e A321732 .
%e A321732 [1 0 0] [1 0 0] [0 1 0] [0 1 0] [0 0 1] [0 0 1]
%e A321732 [0 1 0] [0 0 1] [1 0 0] [0 0 1] [1 0 0] [0 1 0]
%e A321732 [0 0 1] [0 1 0] [0 0 1] [1 0 0] [0 1 0] [1 0 0]
%t A321732 prs2mat[prs_]:=Table[Count[prs,{i,j}],{i,Union[First/@prs]},{j,Union[Last/@prs]}];
%t A321732 multsubs[set_,k_]:=If[k==0,{{}},Join@@Table[Prepend[#,set[[i]]]&/@multsubs[Drop[set,i-1],k-1],{i,Length[set]}]];
%t A321732 Table[Length[Select[multsubs[Tuples[Range[n],2],n],And[Union[First/@#]==Range[Max@@First/@#]==Union[Last/@#],Total/@prs2mat[#]==Total/@Transpose[prs2mat[#]]]&]],{n,5}]
%Y A321732 Cf. A000700, A000701, A006052, A007016, A120732, A319056, A320451, A321718, A321719, A321722, A321733, A321734, A321735, A321736, A321739.
%K A321732 nonn
%O A321732 0,3
%A A321732 _Gus Wiseman_, Nov 18 2018
%E A321732 a(7) onwards from _Ludovic Schwob_, Apr 03 2024