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%I #10 Oct 18 2017 13:27:48
%S 0,2,3,12,30,89,248,706,1995,5652,15998,45297,128240,363074,1027923,
%T 2910236,8239390,23327177,66043368,186980482,529374875,1498754084,
%U 4243238398,12013359841,34011950560,96293859202,272624979363
%N Number of 0..3 arrays of length n with each element differing from at least one neighbor by 2 or more, starting with 0.
%C Column 3 of A221515.
%H R. H. Hardin, <a href="/A221510/b221510.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = a(n-1) +4*a(n-2) +3*a(n-3) +a(n-4).
%F Empirical g.f.: x^2*(2 + x + x^2) / ((1 + x)*(1 - 2*x - 2*x^2 - x^3)). - _Colin Barker_, Oct 18 2017
%e Some solutions for n=6
%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e ..2....2....2....2....2....3....2....2....3....3....2....3....3....2....3....3
%e ..3....0....2....1....2....0....0....3....1....3....3....2....0....1....2....3
%e ..0....2....0....3....0....3....1....1....0....1....1....0....3....3....0....1
%e ..3....2....2....0....3....0....3....1....3....3....0....3....3....3....0....0
%e ..0....0....0....3....1....2....1....3....0....0....2....0....1....1....2....3
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 18 2013
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