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%I #8 Aug 10 2018 17:33:54
%S 0,2,1,9,17,64,171,536,1558,4689,13889,41437,123228,366983,1092232,
%T 3251610,9679073,28813033,85770153,255320984,760038643,2262482568,
%U 6734954798,20048604913,59680661697,177657315701,528850071604
%N Number of 2 X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, without move-in move-out straight through or left turns.
%C Row 2 of A221755.
%H R. H. Hardin, <a href="/A221756/b221756.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = a(n-1) + 6*a(n-2) + a(n-3) - 4*a(n-4).
%F Empirical g.f.: x^2*(2 - x - 4*x^2) / (1 - x - 6*x^2 - x^3 + 4*x^4). - _Colin Barker_, Aug 10 2018
%e Single solution for n=3:
%e ..0..2..1
%e ..1..2..0
%Y Cf. A221755.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 24 2013
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