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A131237
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Number of n X (n+1) matrices with nonnegative integer entries and every row and column sum <= 2.
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2
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1, 6, 79, 1837, 66021, 3374176, 231848191, 20570267229, 2285620096717, 310524073877026, 50598503336716611, 9732804817777566361, 2180831456691952213969, 562835395375423511668692, 165687992856606963112408291, 55166524646338775672718351481, 20620925283916296038124156761241
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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(a).
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LINKS
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MAPLE
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exp((x*y*(3-x*y)/2+(x+y)*(2-x*y)/2)/(1-x*y))/sqrt(1-x*y) ;
coeftayl(%, y=0, n+1) ;
coeftayl(%, x=0, n) ;
%*(n+1)!*n! ;
simplify(%) ;
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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