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 A183521 #7 Jul 22 2025 09:03:31 %S A183521 7,95,543,3507,27609,201833,1521573,11678037,89238523,683029435, %T A183521 5235031077,40141122349,307807564417,2360732530937,18105826441313, %U A183521 138867315400205,1065099011259479,8169267911756541,62658120915577663 %N A183521 Number of nX4 0..2 arrays with each element equal to either the sum mod 3 of its horizontal and vertical neighbors or the sum mod 3 of its diagonal and antidiagonal neighbors. %C A183521 Column 4 of A183526 %H A183521 R. H. Hardin, <a href="/A183521/b183521.txt">Table of n, a(n) for n = 1..200</a> %e A183521 Some solutions for 3X4 %e A183521 ..2..1..2..1....2..1..0..1....1..1..2..2....2..1..0..0....0..0..2..0 %e A183521 ..1..1..0..2....2..2..1..0....0..1..2..0....1..2..2..0....1..0..2..1 %e A183521 ..1..2..0..2....1..2..2..1....1..1..2..2....0..2..0..2....2..1..2..2 %K A183521 nonn %O A183521 1,1 %A A183521 _R. H. Hardin_ Jan 05 2011