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 A222881 #6 Jul 23 2025 03:12:19 %S A222881 15,2150,443510,95867967,20978414941,4643150795564,1036481888251762, %T A222881 232912437941917635,52614561200004212957,11936312777288007185980, %U A222881 2717468404561524996790251,620503805193057253513443782 %N A222881 Number of 4Xn 0..3 arrays with no more than floor(4Xn/2) elements equal to at least one horizontal or antidiagonal neighbor, with new values introduced in row major 0..3 order. %C A222881 Row 4 of A222878 %H A222881 R. H. Hardin, <a href="/A222881/b222881.txt">Table of n, a(n) for n = 1..16</a> %e A222881 Some solutions for n=3 %e A222881 ..0..0..1....0..1..0....0..1..0....0..1..0....0..0..0....0..1..0....0..0..1 %e A222881 ..1..2..2....0..2..0....0..1..0....0..2..1....1..2..1....0..2..2....1..2..1 %e A222881 ..1..2..1....3..0..3....0..1..2....1..1..3....1..1..2....1..0..1....1..0..0 %e A222881 ..3..0..2....1..3..3....3..1..3....0..3..1....3..0..2....3..0..3....1..1..0 %K A222881 nonn %O A222881 1,1 %A A222881 _R. H. Hardin_ Mar 08 2013