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 A333681 #9 Apr 03 2020 12:34:15 %S A333681 1,2,3,4,6,8,19,44,314,7526,846993,324127860,403254094632, %T A333681 1555631972009430,19731915624463099553,791773335030637885025288, %U A333681 107432353216118868234728540268,47049030539260648478475949282317452,71364337698829887974206671525372672234855 %N A333681 Number of non-isomorphic n X n binary matrices with all row and column sums equal up to permutation of rows and columns. %F A333681 a(n) = A000519(n) + 1. %e A333681 The a(2) = 3 matrices are: %e A333681 [0 0] [0 1] [1 1] %e A333681 [0 0] [1 0] [1 1] %Y A333681 Row sums of A133687. %Y A333681 Cf. A000519, A067209, A333160. %K A333681 nonn %O A333681 0,2 %A A333681 _Andrew Howroyd_, Apr 01 2020