A131237 Number of n X (n+1) matrices with nonnegative integer entries and every row and column sum <= 2.

1, 6, 79, 1837, 66021, 3374176, 231848191, 20570267229, 2285620096717, 310524073877026, 50598503336716611, 9732804817777566361, 2180831456691952213969, 562835395375423511668692, 165687992856606963112408291, 55166524646338775672718351481, 20620925283916296038124156761241

Offset: 0

Author

Vladeta Jovovic, Jun 20 2007

Keywords

• easy
• nonn

References

• R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(a).

Crossrefs

Cf. A049088, A131235, A131236.

Programs

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