# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a230813 Showing 1-1 of 1 %I A230813 #9 Mar 17 2018 07:10:13 %S A230813 0,0,2,0,2,12,18,56,170,420,1162,3200,8562,23292,63298,171336,464890, %T A230813 1261140,3419322,9274000,25152322,68211372,184993778,501712216, %U A230813 1360654410,3690150660,10007829482,27141578400,73608971282,199630236252 %N A230813 Number of n X 2 0..2 arrays x(i,j) with each element horizontally or vertically next to at least one element with value (x(i,j)+1) mod 3 and at least one element with value (x(i,j)-1) mod 3, and upper left element zero. %C A230813 Column 2 of A230819. %H A230813 R. H. Hardin, Table of n, a(n) for n = 1..210 %F A230813 Empirical: a(n) = 2*a(n-1) + a(n-2) + 4*a(n-3) - 4*a(n-4). %F A230813 Empirical g.f.: 2*x^3*(1 - 2*x) / (1 - 2*x - x^2 - 4*x^3 + 4*x^4). - _Colin Barker_, Mar 17 2018 %e A230813 All solutions for n=5: %e A230813 ..0..1....0..2 %e A230813 ..2..2....1..1 %e A230813 ..1..0....2..0 %e A230813 ..2..2....1..1 %e A230813 ..0..1....0..2 %Y A230813 Cf. A230819. %K A230813 nonn %O A230813 1,3 %A A230813 _R. H. Hardin_, Oct 30 2013 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE