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 A199645 #7 Jul 22 2025 13:21:15 %S A199645 6,1384,134748,15066222,1614250077,176701683386,19161971644783, %T A199645 2085499380111100,226676302441401393,24649864713781053665, %U A199645 2680046304287719376722,291407720701800854792287 %N A199645 Number of nX6 0..2 arrays with values 0..2 introduced in row major order and each element equal to one or two horizontal and vertical neighbors. %C A199645 Column 6 of A199647 %H A199645 R. H. Hardin, <a href="/A199645/b199645.txt">Table of n, a(n) for n = 1..30</a> %e A199645 Some solutions for n=3 %e A199645 ..0..1..1..0..0..0....0..1..2..2..2..2....0..0..1..1..2..1....0..1..0..2..1..2 %e A199645 ..0..1..0..2..2..2....0..1..2..0..0..2....2..0..2..2..2..1....0..1..0..2..1..2 %e A199645 ..0..0..0..1..1..2....0..1..1..2..2..2....2..0..0..1..1..1....2..2..2..2..1..2 %K A199645 nonn %O A199645 1,1 %A A199645 _R. H. Hardin_ Nov 08 2011