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A199649 Number of n X 2 0..2 arrays with values 0..2 introduced in row major order and each element equal to no more than two horizontal and vertical neighbors.

%I A199649 #9 Mar 02 2018 11:27:16
%S A199649 2,14,113,953,8037,67774,571530,4819638,40643380,342740340,2890284724,
%T A199649 24373395288,205537673480,1733272476824,14616461440144,
%U A199649 123258718919184,1039424750772560,8765333779162336,73916920107029408,623331776719986016
%N A199649 Number of n X 2 0..2 arrays with values 0..2 introduced in row major order and each element equal to no more than two horizontal and vertical neighbors.
%C A199649 Column 2 of A199655.
%H A199649 R. H. Hardin, <a href="/A199649/b199649.txt">Table of n, a(n) for n = 1..200</a>
%F A199649 Empirical: a(n) = 8*a(n-1) + 4*a(n-2) - 2*a(n-3) - 8*a(n-4) for n>6.
%F A199649 Empirical g.f.: x*(2 - 2*x - 7*x^2 - 3*x^3 + 5*x^4 + 4*x^5) / (1 - 8*x - 4*x^2 + 2*x^3 + 8*x^4). - _Colin Barker_, Mar 02 2018
%e A199649 Some solutions for n=3:
%e A199649 ..0..1....0..0....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..0
%e A199649 ..0..2....1..1....2..2....0..1....1..2....2..0....0..1....2..2....0..2....1..0
%e A199649 ..1..2....2..1....0..0....2..1....1..2....1..2....0..2....0..2....2..0....1..0
%Y A199649 Cf. A199655.
%K A199649 nonn
%O A199649 1,1
%A A199649 _R. H. Hardin_, Nov 08 2011