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 A239979 #7 Jun 02 2025 09:35:41 %S A239979 1,3,13,171,7113,652346,226886115,198719581101 %N A239979 Number of n X n 0..3 arrays with no element equal to zero plus the sum of elements to its left or two plus the sum of the elements above it or one plus the sum of the elements diagonally to its northwest, modulo 4. %C A239979 Diagonal of A239986 %e A239979 Some solutions for n=4 %e A239979 ..3..0..0..0....3..0..0..0....3..0..0..0....3..0..0..0....3..0..0..0 %e A239979 ..2..3..3..3....2..3..0..0....2..1..0..0....2..1..0..0....2..3..3..3 %e A239979 ..2..0..0..3....2..0..0..0....2..0..3..0....2..0..0..3....2..0..0..3 %e A239979 ..3..0..0..1....2..0..1..1....3..0..0..1....3..1..1..3....3..0..2..2 %K A239979 nonn %O A239979 1,2 %A A239979 _R. H. Hardin_, Mar 30 2014