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%I #8 Aug 03 2018 08:22:28
%S 0,4,24,169,1155,7921,54288,372100,2550408,17480761,119814915,
%T 821223649,5628750624,38580030724,264431464440,1812440220361,
%U 12422650078083,85146110326225,583600122205488,4000054745112196,27416783093579880
%N Number of 2 X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor.
%C Row 2 of A221087.
%H R. H. Hardin, <a href="/A221088/b221088.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 7*a(n-1) - 7*a(n-3) + a(n-4).
%F Empirical g.f.: x^2*(2 - x)^2 / ((1 - x)*(1 + x)*(1 - 7*x + x^2)). - _Colin Barker_, Aug 03 2018
%e Some solutions for n=3:
%e ..0..1..0....0..1..1....1..2..0....1..3..1....1..1..0....1..3..0....1..2..1
%e ..2..3..0....0..3..1....1..2..0....0..1..0....0..3..1....0..1..1....0..2..0
%Y Cf. A221087.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 01 2013
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