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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, 1, 3, 9, 33, 142, 742, 4454, 30516, 233574, 1972430, 18190806, 181774873, 1955268162, 22516241557, 276294103003, 3598106433662, 49551992313623, 719398127720459, 10979514511427858, 175716291405379723, 2942195925987952412, 51436169813668249174, 937106275320950472387, 17761791825490936694507 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 21 17:13 EDT 2022. Contains 353921 sequences. (Running on oeis4.)