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 A333886 #8 Apr 09 2020 03:13:55 %S A333886 1,1,5,12,33,74,163,319,596,1044,1754,2820,4394,6629,9756,14018,19743, %T A333886 27286,37111,49707,65699,85756,110691,141382,178882,224309,278990, %U A333886 344342,422000,513718,621506,747493,894105,1063920,1259823,1484886,1742533,2036377,2370431,2748936,3176544 %N A333886 Number of non-isomorphic 4 X 4 nonnegative integer symmetric matrices with all row and column sums equal to n up to permutations of rows and columns. %e A333886 The a(2) = 5 matrices are: %e A333886 [0 0 0 2] [0 0 0 2] [0 0 1 1] [0 0 1 1] [0 0 1 1] %e A333886 [0 0 2 0] [0 1 1 0] [0 0 1 1] [0 1 0 1] [0 2 0 0] %e A333886 [0 2 0 0] [0 1 1 0] [1 1 0 0] [1 0 1 0] [1 0 0 1] %e A333886 [2 0 0 0] [2 0 0 0] [1 1 0 0] [1 1 0 0] [1 0 1 0] %e A333886 . %e A333886 The a(3) = 12 matrices are: %e A333886 [0 0 0 3] [0 0 1 2] [0 0 1 2] [0 0 1 2] [0 0 1 2] [0 1 1 1] %e A333886 [0 0 3 0] [0 0 2 1] [0 1 1 1] [0 1 2 0] [0 2 1 0] [1 0 1 1] %e A333886 [0 3 0 0] [1 2 0 0] [1 1 1 0] [1 2 0 0] [1 1 0 1] [1 1 0 1] %e A333886 [3 0 0 0] [2 1 0 0] [2 1 0 0] [2 0 0 1] [2 0 1 0] [1 1 1 0] %e A333886 . %e A333886 [0 0 0 3] [0 0 1 2] [0 0 1 2] [0 0 1 2] [0 1 1 1] [1 0 1 1] %e A333886 [0 1 2 0] [0 2 1 0] [0 3 0 0] [0 3 0 0] [1 1 0 1] [0 3 0 0] %e A333886 [0 2 1 0] [1 1 1 0] [1 0 1 1] [1 0 2 0] [1 0 2 0] [1 0 1 1] %e A333886 [3 0 0 0] [2 0 0 1] [2 0 1 0] [2 0 0 1] [1 1 0 1] [1 0 1 1] %Y A333886 Row n=4 of A333737. %K A333886 nonn %O A333886 0,3 %A A333886 _Andrew Howroyd_, Apr 08 2020