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 A222681 #5 Jul 23 2025 02:55:23 %S A222681 5,5,11,58,142,2398,6463,146947,401552,9871237,27759999,675112590, %T A222681 1962193874,46428879519,139050595341,3201678397354,9862902257940, %U A222681 221229238222335,700012077054917 %N A222681 Number of 3Xn 0..3 arrays with no more than floor(3Xn/2) elements unequal to at least one horizontal, diagonal or antidiagonal neighbor, with new values introduced in row major 0..3 order. %C A222681 Row 3 of A222679 %e A222681 Some solutions for n=3 %e A222681 ..0..1..2....0..1..1....0..0..0....0..0..0....0..0..1....0..1..0....0..0..0 %e A222681 ..1..1..1....1..1..1....0..0..0....0..0..0....0..0..0....1..1..1....1..0..0 %e A222681 ..1..1..1....1..1..1....0..0..0....0..0..1....0..0..0....1..1..1....0..0..0 %K A222681 nonn %O A222681 1,1 %A A222681 _R. H. Hardin_ Feb 28 2013