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A049088
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Number of n X n matrices with nonnegative integer entries and every row and column sum <= 2.
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4
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1, 3, 26, 451, 12951, 551681, 32512618, 2525962461, 249675308081, 30551602194811, 4528860725614746, 799069823975939363, 165374947602000265231, 39654053930039468491521, 10900817711883556591556906, 3404265715022353551494548021, 1198175785461867097633422235713
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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REFERENCES
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R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(b).
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LINKS
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FORMULA
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Stanley gives an explicit generating function.
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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