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A333889
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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.
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1
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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
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OFFSET
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0,3
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LINKS
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EXAMPLE
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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]
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[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]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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