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 A212042 #6 Jun 02 2025 07:54:48 %S A212042 0,0,5,447,94131,5054845,109065807,1339229741,11235618109 %N A212042 Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any element within a city block distance of two, and containing the value n(n+1)/2-5. %C A212042 Column 4 of A212044 %e A212042 Some solutions for n=4 %e A212042 ..0........0........0........0........0........0........0........0 %e A212042 ..1.2......1.2......1.2......1.2......1.2......1.2......1.2......1.2 %e A212042 ..3.4.0....3.0.4....3.4.0....3.0.4....3.4.5....3.4.5....3.0.4....3.4.5 %e A212042 ..0.5.3.4..5.1.2.5..5.6.3.5..5.6.7.5..5.0.6.2..2.1.0.2..5.1.6.2..6.7.2.1 %K A212042 nonn %O A212042 1,3 %A A212042 _R. H. Hardin_ Apr 28 2012