A049088 Number of n X n matrices with nonnegative integer entries and every row and column sum <= 2.

1, 3, 26, 451, 12951, 551681, 32512618, 2525962461, 249675308081, 30551602194811, 4528860725614746, 799069823975939363, 165374947602000265231, 39654053930039468491521, 10900817711883556591556906, 3404265715022353551494548021, 1198175785461867097633422235713

Offset: 0

Author

N. J. A. Sloane, Jan 23 2000

Keywords

• nonn
• easy
• nice

References

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

Crossrefs

Cf. A073178, A073179. Diagonal of A131235.

Formula

Stanley gives an explicit generating function.