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%I #4 Jan 11 2013 05:37:21
%S 1,577,33873,2460824,162430981,10794156688,711858713069,
%T 46910596287335,3089778765626866,203426990390736036,
%U 13389504827335440162,881130781309712234876,57978558022828544235124,3814742757245230038689495
%N Number of 4Xn arrays of occupancy after each element stays put or moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2
%C Row 4 of A221328
%H R. H. Hardin, <a href="/A221331/b221331.txt">Table of n, a(n) for n = 1..27</a>
%e Some solutions for n=3
%e ..2..0..1....1..2..0....2..1..1....1..1..1....1..1..0....2..0..1....1..1..2
%e ..2..2..0....1..1..0....1..0..0....1..0..2....2..0..0....0..2..1....1..2..1
%e ..1..0..2....1..1..0....1..2..0....0..2..0....2..2..1....1..2..1....0..1..2
%e ..0..2..0....1..2..2....0..2..2....1..2..1....1..0..2....1..1..0....0..0..1
%K nonn
%O 1,2
%A _R. H. Hardin_ Jan 11 2013