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%I #7 Aug 04 2018 14:33:10
%S 0,4,4,25,52,196,520,1681,4840,14884,44044,133225,397852,1196836,
%T 3585040,10764961,32278480,96864964,290545684,871725625,2615029252,
%U 7845353476,23535617560,70607649841,211821620920,635467254244,1906397776924
%N Number of 2 X n arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with every occupancy equal to zero or two.
%C Row 2 of A221275.
%H R. H. Hardin, <a href="/A221276/b221276.txt">Table of n, a(n) for n = 1..94</a>
%F Empirical: a(n) = 4*a(n-1) - 12*a(n-3) + 9*a(n-4).
%F Empirical g.f.: x^2*(2 - 3*x)^2 / ((1 - x)*(1 - 3*x)*(1 - 3*x^2)). - _Colin Barker_, Aug 04 2018
%e Some solutions for n=4:
%e ..0..0..0..2....0..2..2..0....2..2..2..0....2..0..0..0....0..2..2..0
%e ..2..2..2..0....2..0..0..2....0..0..0..2....0..2..2..2....0..2..2..0
%Y Cf. A221275.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 09 2013