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 A266021 #4 Dec 20 2015 07:10:30 %S A266021 5,42,91,577,3796,19688,110924,656555,3732300,21344656,123330565, %T A266021 708246405,4066193034,23408646708,134627655119,773992993358, %U A266021 4452175085918,25607065587568,147270467464058,847048745101385 %N A266021 Number of nX4 integer arrays with each element equal to the number of horizontal, vertical and antidiagonal neighbors exactly one smaller than itself. %C A266021 Column 4 of A266025. %H A266021 R. H. Hardin, <a href="/A266021/b266021.txt">Table of n, a(n) for n = 1..210</a> %e A266021 Some solutions for n=4 %e A266021 ..1..0..0..1....0..0..1..1....0..1..1..0....0..0..1..1....0..2..1..0 %e A266021 ..1..2..1..1....0..2..2..0....2..3..2..0....0..2..2..0....0..1..1..1 %e A266021 ..2..2..2..0....1..2..0..0....1..2..1..2....1..3..2..1....2..1..1..1 %e A266021 ..1..0..0..0....1..0..0..0....0..2..1..0....1..0..1..2....0..2..0..1 %Y A266021 Cf. A266025. %K A266021 nonn %O A266021 1,1 %A A266021 _R. H. Hardin_, Dec 20 2015