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 A241399 #6 Jun 02 2025 10:07:49 %S A241399 4,13,29,85,201,689,1929,4068,11963,33651,80035,231111,606571,1542322, %T A241399 4407947,11308092,29789742,82990169,213582987,572318731,1556503937, %U A241399 4056412623,10923983311,29272912317,77140259839,207516834784 %N A241399 Number of 3Xn 0..3 arrays with no element equal to zero plus the sum of elements to its left or one 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 A241399 Row 3 of A241397 %H A241399 R. H. Hardin, <a href="/A241399/b241399.txt">Table of n, a(n) for n = 1..143</a> %e A241399 Some solutions for n=4 %e A241399 ..2..3..2..2....3..2..2..2....3..2..3..3....2..3..3..2....2..3..3..3 %e A241399 ..2..1..2..0....1..0..0..0....1..2..1..2....2..1..2..2....2..3..2..2 %e A241399 ..3..0..0..0....2..0..0..0....3..2..0..0....2..0..0..0....2..1..0..0 %K A241399 nonn %O A241399 1,1 %A A241399 _R. H. Hardin_, Apr 20 2014