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 A206390 #8 May 17 2021 15:47:04 %S A206390 1,1,26,1931,170796,21983256,3889732730,998388746378 %N A206390 Number of n X n 0..5 arrays with no element equal to another within a city block distance of two, and new values 0..5 introduced in row major order. %C A206390 Diagonal of A206396. %e A206390 Some solutions for n=4 %e A206390 ..0..1..2..0....0..1..2..3....0..1..2..0....0..1..2..3....0..1..2..3 %e A206390 ..2..3..4..1....3..4..5..0....2..3..4..5....2..3..4..5....4..3..5..4 %e A206390 ..1..5..0..2....1..0..3..1....4..5..0..1....4..5..0..1....5..2..0..1 %e A206390 ..4..2..3..4....2..5..4..2....0..1..2..3....3..1..2..3....0..1..4..3 %Y A206390 Cf. A206396. %K A206390 nonn %O A206390 1,3 %A A206390 _R. H. Hardin_ Feb 07 2012