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%I #8 Mar 19 2018 16:51:35
%S 1,3,26,451,12951,551681,32512618,2525962461,249675308081,
%T 30551602194811,4528860725614746,799069823975939363,
%U 165374947602000265231,39654053930039468491521,10900817711883556591556906,3404265715022353551494548021,1198175785461867097633422235713
%N Number of n X n matrices with nonnegative integer entries and every row and column sum <= 2.
%D R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(b).
%F Stanley gives an explicit generating function.
%Y Cf. A073178, A073179. Diagonal of A131235.
%K nonn,easy,nice
%O 0,2
%A _N. J. A. Sloane_, Jan 23 2000
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