This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A049088 #8 Mar 19 2018 16:51:35 %S A049088 1,3,26,451,12951,551681,32512618,2525962461,249675308081, %T A049088 30551602194811,4528860725614746,799069823975939363, %U A049088 165374947602000265231,39654053930039468491521,10900817711883556591556906,3404265715022353551494548021,1198175785461867097633422235713 %N A049088 Number of n X n matrices with nonnegative integer entries and every row and column sum <= 2. %D A049088 R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(b). %F A049088 Stanley gives an explicit generating function. %Y A049088 Cf. A073178, A073179. Diagonal of A131235. %K A049088 nonn,easy,nice %O A049088 0,2 %A A049088 _N. J. A. Sloane_, Jan 23 2000