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 A252923 #11 Feb 07 2019 15:24:16 %S A252923 0,0,1,615,84910,8241540,759337545,73117894428,7578889491370, %T A252923 848729993032718,102072779621746876,13069744040275286234, %U A252923 1766655687081261435255,250232365919081938956865,36910187948533534644694094 %N A252923 Number of n X n nonnegative integer arrays with upper left 0 and lower right n+n-6 and value increasing by 0 or 1 with every step right or down. %H A252923 Alois P. Heinz, <a href="/A252923/b252923.txt">Table of n, a(n) for n = 1..20</a> (first 15 terms from R. H. Hardin) %e A252923 Some solutions for n=4 %e A252923 ..0..0..1..1....0..0..1..1....0..1..1..1....0..0..1..2....0..0..0..1 %e A252923 ..0..0..1..2....0..0..1..2....0..1..2..2....0..1..1..2....0..0..1..2 %e A252923 ..0..1..2..2....1..1..1..2....0..1..2..2....1..1..1..2....0..1..2..2 %e A252923 ..1..1..2..2....1..2..2..2....1..1..2..2....1..1..1..2....1..2..2..2 %Y A252923 Diagonal of A252930. %K A252923 nonn %O A252923 1,4 %A A252923 _R. H. Hardin_, Dec 24 2014