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.

1, 1, 3, 9, 33, 142, 742, 4454, 30516, 233574, 1972430, 18190806, 181774873, 1955268162, 22516241557, 276294103003, 3598106433662, 49551992313623, 719398127720459, 10979514511427858, 175716291405379723, 2942195925987952412, 51436169813668249174, 937106275320950472387, 17761791825490936694507

Offset

0,3

Links

Table of n, a(n) for n=0..24.

Example

The a(3) = 9 matrices are:
   [0 0 4]  [0 1 3]  [0 1 3]  [0 2 2]  [0 2 2]
   [0 4 0]  [1 2 1]  [1 3 0]  [2 0 2]  [2 1 1]
   [4 0 0]  [3 1 0]  [3 0 1]  [2 2 0]  [2 1 1]
.
   [1 0 3]  [1 1 2]  [1 1 2]  [2 0 2]
   [0 4 0]  [1 2 1]  [1 3 0]  [0 4 0]
   [3 0 1]  [2 1 1]  [2 0 2]  [2 0 2]

Crossrefs

Column k=4 of A333737.

Sequence in context: A193110 A001930 A049425 * A277395 A012584 A101899

Adjacent sequences: A333886 A333887 A333888 * A333890 A333891 A333892

Keyword

nonn

Author

Andrew Howroyd, Apr 08 2020

Status

approved