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A131237
Number of n X (n+1) matrices with nonnegative integer entries and every row and column sum <= 2.
2
1, 6, 79, 1837, 66021, 3374176, 231848191, 20570267229, 2285620096717, 310524073877026, 50598503336716611, 9732804817777566361, 2180831456691952213969, 562835395375423511668692, 165687992856606963112408291, 55166524646338775672718351481, 20620925283916296038124156761241
OFFSET
0,2
REFERENCES
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(a).
MAPLE
A131237 := proc(n)
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(%) ;
end proc: # R. J. Mathar, Sep 30 2011
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Jun 20 2007
STATUS
approved