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%I #13 Feb 20 2018 07:19:33
%S 2,10,36,126,454,1632,5854,21010,75412,270662,971438,3486624,12513958,
%T 44914250,161203204,578579694,2076599286,7453190368,26750489166,
%U 96011055010,344596415668,1236802258678,4439047411742,15932330156576
%N Number of n X 2 binary arrays with every one adjacent to another one horizontally or vertically.
%C Column 2 of A202802.
%H R. H. Hardin, <a href="/A202796/b202796.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 3*a(n-1) + a(n-2) + 4*a(n-3).
%F Empirical g.f.: 2*x*(1 + 2*x + 2*x^2) / (1 - 3*x - x^2 - 4*x^3). - _Colin Barker_, Feb 20 2018
%e Some solutions for n=5:
%e ..0..1....0..0....0..1....1..0....0..0....1..0....1..1....0..1....0..1....1..0
%e ..0..1....1..0....1..1....1..0....0..0....1..0....1..1....1..1....1..1....1..1
%e ..1..1....1..1....1..1....1..1....0..1....0..0....1..0....0..0....1..0....0..1
%e ..1..1....0..1....1..0....1..0....0..1....0..1....0..1....1..0....0..0....1..0
%e ..1..0....1..1....1..0....1..0....0..0....0..1....1..1....1..1....0..0....1..0
%Y Cf. A202802.
%K nonn
%O 1,1
%A _R. H. Hardin_, Dec 24 2011
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