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 A211908 #6 Apr 16 2023 20:45:59 %S A211908 0,0,42,6927,605769,18239150,281228042,2788818593,20221781939 %N A211908 Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any horizontal or vertical neighbor, and containing the value n(n+1)/2-5. %C A211908 Column 4 of A211910. %e A211908 Some solutions for n=4 %e A211908 ..0........0........0........0........0........0........0........0 %e A211908 ..1.2......1.2......1.2......1.2......1.2......1.2......1.2......1.2 %e A211908 ..3.4.5....3.1.4....2.0.3....3.4.1....0.3.4....3.4.3....3.4.5....2.3.4 %e A211908 ..4.5.6.2..5.6.1.4..4.1.5.3..2.5.6.4..1.5.6.3..5.3.0.4..5.1.3.4..3.4.5.6 %Y A211908 Cf. A211910. %K A211908 nonn %O A211908 1,3 %A A211908 _R. H. Hardin_, Apr 25 2012