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%I #4 Jan 14 2013 05:23:19
%S 0,0,13,1198,52320,2204556,86673898,3361458245,128992693561,
%T 4928816080380,187851827622672,7150418585672281,271982464009887803,
%U 10341601574159713990,393139667142067892978,14943725056237306101598
%N Number of 4Xn arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no 2-loops and with no occupancy greater than 2
%C Row 4 of A221388
%H R. H. Hardin, <a href="/A221390/b221390.txt">Table of n, a(n) for n = 1..21</a>
%e Some solutions for n=3
%e ..0..2..1....0..2..1....0..2..1....0..2..1....0..2..0....0..2..1....0..2..0
%e ..0..2..1....0..2..1....0..2..0....1..2..1....1..2..1....1..2..1....1..2..1
%e ..1..2..1....1..2..0....1..2..1....0..2..1....1..2..1....0..2..0....0..2..1
%e ..0..2..0....1..2..0....1..2..0....0..2..0....0..2..0....1..2..0....1..2..0
%K nonn
%O 1,3
%A _R. H. Hardin_ Jan 14 2013