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%I #4 Jan 06 2013 19:56:24
%S 0,16,30,2116,22268,488601,7356420,132273001,2175160988,37343243536,
%T 627439570380,10652755988736,179923226827008,3046558564618321,
%U 51520912019433840,871812703964410321,14747896839403221578
%N Number of 3Xn arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2
%C Row 3 of A221255
%H R. H. Hardin, <a href="/A221257/b221257.txt">Table of n, a(n) for n = 1..36</a>
%F Empirical: a(n) = 21*a(n-1) +21*a(n-2) -1891*a(n-3) +4713*a(n-4) +31527*a(n-5) -98973*a(n-6) -92217*a(n-7) +299577*a(n-8) -27117*a(n-9) +103383*a(n-10) -393*a(n-11) +6211*a(n-12) +69*a(n-13) +69*a(n-14) +a(n-15) for n>18
%e Some solutions for n=3
%e ..0..2..1....0..2..0....1..2..0....0..2..2....1..2..0....1..2..0....0..2..2
%e ..0..2..0....1..2..0....0..2..1....0..2..0....0..2..0....1..2..1....0..2..1
%e ..1..2..1....1..2..1....1..2..0....1..2..0....1..2..1....0..2..0....0..2..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Jan 06 2013
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