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%I #7 May 23 2013 07:06:47
%S 1,4,9,23,57,142,353,878,2183,5428,13496,33556,83432,207441,515770,
%T 1282382,3188443
%N Square root of number of nX4 arrays of occupancy after each element moves to some horizontal or vertical neighbor, with every occupancy equal to zero or two
%C Column 4 of A221314
%F Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - a(n-3) - 2*a(n-4) - a(n-5). - _Vaclav Kotesovec_, May 23 2013
%e Some solutions for n=3
%e ..2..2..0..0....2..2..2..0....2..2..0..0....0..2..2..0....0..2..2..0
%e ..0..2..0..2....2..0..0..0....2..0..0..2....2..2..0..0....0..0..0..0
%e ..0..2..0..2....0..0..2..2....0..0..2..2....0..0..2..2....2..2..2..2
%K nonn
%O 1,2
%A _R. H. Hardin_ Jan 10 2013