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%I #4 Jan 02 2013 19:45:34
%S 4,289,12544,643204,31203396,1539699121,75512292025,3709710975721,
%T 182118668668225,8941989810789025,439009303948483984,
%U 21553427021714858449,1058163003670012270144,51950295646215686851681
%N Number of nX4 arrays of occupancy after each element moves to some horizontal or vertical neighbor, with no occupancy greater than 2
%C Column 4 of A221139
%H R. H. Hardin, <a href="/A221135/b221135.txt">Table of n, a(n) for n = 1..23</a>
%e Some solutions for n=3
%e ..2..2..2..1....2..1..1..1....1..2..2..0....0..1..2..0....2..2..1..0
%e ..1..0..1..1....2..1..0..1....1..0..1..2....2..2..1..0....0..1..1..1
%e ..1..0..0..1....0..2..1..0....1..1..0..1....0..1..2..1....1..2..0..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jan 02 2013