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 A333891 #5 Apr 18 2020 17:16:26 %S A333891 1,2,3,4,10,48,814,35048,4749917,1991695464,2744917591408, %T A333891 12259363447566918,187472413992607944600,9519583446974164009046934, %U A333891 1702816871202402787766029201942,1029212386646920125804443494952269006,2240000312861150532290111516186650669871299 %N A333891 Number of nonequivalent n X n binary matrices with an equal number of ones in every row and column up to permutation of rows. %H A333891 Andrew Howroyd, <a href="/A333891/b333891.txt">Table of n, a(n) for n = 0..20</a> %e A333891 The a(4) = 10 matrices are: %e A333891 [0 0 0 0] [0 0 0 1] [0 0 1 1] [0 1 0 1] [0 1 1 0] %e A333891 [0 0 0 0] [0 0 1 0] [0 0 1 1] [0 1 0 1] [0 1 1 0] %e A333891 [0 0 0 0] [0 1 0 0] [1 1 0 0] [1 0 1 0] [1 0 0 1] %e A333891 [0 0 0 0] [1 0 0 0] [1 1 0 0] [1 0 1 0] [1 0 0 1] %e A333891 . %e A333891 [0 0 1 1] [0 0 1 1] [0 1 0 1] [0 1 1 1] [1 1 1 1] %e A333891 [0 1 1 0] [0 1 0 1] [0 1 1 0] [1 0 1 1] [1 1 1 1] %e A333891 [1 0 0 1] [1 0 1 0] [1 0 0 1] [1 1 0 1] [1 1 1 1] %e A333891 [1 1 0 0] [1 1 0 0] [1 0 1 0] [1 1 1 0] [1 1 1 1] %Y A333891 Row sums of A260340. %K A333891 nonn %O A333891 0,2 %A A333891 _Andrew Howroyd_, Apr 18 2020