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 A211915 #6 Jun 02 2025 07:52:01 %S A211915 0,0,10,1732,1085432,146208485,6410611003,140836842878 %N A211915 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, vertical, diagonal or antidiagonal neighbor, and containing the value n(n+1)/2-6. %C A211915 Column 5 of A211916 %e A211915 Some solutions for n=4 %e A211915 ..0........0........0........0........0........0........0........0 %e A211915 ..1.2......1.2......1.2......1.2......1.2......1.2......1.2......1.2 %e A211915 ..3.4.1....3.0.3....0.3.4....3.4.0....3.4.5....3.0.4....0.3.1....3.0.4 %e A211915 ..1.0.5.3..2.4.5.6..5.1.6.3..5.1.5.3..2.1.0.3..5.2.6.0..2.4.2.4..4.5.3.6 %K A211915 nonn %O A211915 1,3 %A A211915 _R. H. Hardin_ Apr 25 2012