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 A215899 #7 Jul 22 2025 23:27:02 %S A215899 1,1,15,602,2387217,33093356640,148049909203591059 %N A215899 Number of diagonal and antidiagonal neighbor colorings of the even squares of an n X n array with new integer colors introduced in row major order. %C A215899 Diagonal of A215904 %e A215899 Some solutions for n=3 %e A215899 ..0..x..0....0..x..0....0..x..0....0..x..1....0..x..1....0..x..1....0..x..1 %e A215899 ..x..1..x....x..1..x....x..1..x....x..2..x....x..2..x....x..2..x....x..2..x %e A215899 ..2..x..2....2..x..0....2..x..3....1..x..3....3..x..3....0..x..0....1..x..0 %K A215899 nonn %O A215899 1,3 %A A215899 _R. H. Hardin_ Aug 26 2012