cp's OEIS Frontend

A333889 Number of non-isomorphic n X n nonnegative integer symmetric matrices with all row and column sums equal to 4 up to permutations of rows and columns.

%I A333889 #4 Apr 08 2020 21:14:32
%S A333889 1,1,3,9,33,142,742,4454,30516,233574,1972430,18190806,181774873,
%T A333889 1955268162,22516241557,276294103003,3598106433662,49551992313623,
%U A333889 719398127720459,10979514511427858,175716291405379723,2942195925987952412,51436169813668249174,937106275320950472387,17761791825490936694507
%N A333889 Number of non-isomorphic n X n nonnegative integer symmetric matrices with all row and column sums equal to 4 up to permutations of rows and columns.
%e A333889 The a(3) = 9 matrices are:
%e A333889    [0 0 4]  [0 1 3]  [0 1 3]  [0 2 2]  [0 2 2]
%e A333889    [0 4 0]  [1 2 1]  [1 3 0]  [2 0 2]  [2 1 1]
%e A333889    [4 0 0]  [3 1 0]  [3 0 1]  [2 2 0]  [2 1 1]
%e A333889 .
%e A333889    [1 0 3]  [1 1 2]  [1 1 2]  [2 0 2]
%e A333889    [0 4 0]  [1 2 1]  [1 3 0]  [0 4 0]
%e A333889    [3 0 1]  [2 1 1]  [2 0 2]  [2 0 2]
%Y A333889 Column k=4 of A333737.
%K A333889 nonn
%O A333889 0,3
%A A333889 _Andrew Howroyd_, Apr 08 2020