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 A240040 #7 Jun 02 2025 09:38:41 %S A240040 2,4,26,346,7514,640643,104619164,49892724623 %N A240040 Number of n X n 0..3 arrays with no element equal to zero plus the sum of elements to its left or zero plus the sum of the elements above it or zero plus the sum of the elements diagonally to its northwest or one plus the sum of the elements antidiagonally to its northeast, modulo 4. %C A240040 Diagonal of A240046 %e A240040 Some solutions for n=3 %e A240040 ..2..3..2....2..3..2....2..3..2....3..2..2....2..3..3....2..3..3....2..3..2 %e A240040 ..1..0..0....3..0..0....1..0..0....1..0..3....3..1..2....3..1..2....3..0..0 %e A240040 ..1..2..0....2..0..3....1..0..3....2..3..2....3..2..2....3..1..2....2..0..0 %K A240040 nonn %O A240040 1,1 %A A240040 _R. H. Hardin_, Mar 31 2014