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 A240147 #7 Jun 02 2025 09:40:01 %S A240147 2,5,20,676,11742,1608415,417799464 %N A240147 Number of n X n 0..3 arrays with no element equal to one plus the sum of elements to its left or one plus the sum of the elements above it or one plus the sum of the elements diagonally to its northwest or zero plus the sum of the elements antidiagonally to its northeast, modulo 4. %C A240147 Diagonal of A240153 %e A240147 Some solutions for n=4 %e A240147 ..2..2..3..2....2..2..3..2....2..2..3..2....2..2..3..2....3..2..3..3 %e A240147 ..0..2..1..1....0..2..1..1....0..2..1..1....0..2..1..1....3..1..2..2 %e A240147 ..2..2..2..2....2..0..2..3....2..0..0..1....2..2..3..3....2..2..0..3 %e A240147 ..3..2..0..1....0..0..0..2....2..2..3..3....0..2..1..1....2..0..0..2 %K A240147 nonn %O A240147 1,1 %A A240147 _R. H. Hardin_, Apr 02 2014