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Number of -2..2 arrays x(0..n-1) of n elements with zero sum, and adjacent elements not equal modulo three (with -1 modulo 3 = 2)
1

%I #6 Mar 31 2012 12:36:37

%S 1,4,12,24,82,232,654,2044,6096,18564,57500,177032,550098,1715956,

%T 5359158,16799508,52760640,165976252,523094304,1650781728,5216112586,

%U 16501009804,52252555938,165618780196,525388548976,1667965025692

%N Number of -2..2 arrays x(0..n-1) of n elements with zero sum, and adjacent elements not equal modulo three (with -1 modulo 3 = 2)

%C Column 2 of A199909

%H R. H. Hardin, <a href="/A199903/b199903.txt">Table of n, a(n) for n = 1..200</a>

%e Some solutions for n=6

%e ..1....0....0....1....1....1....1....1...-1...-1...-1....0....0...-2....1...-1

%e ..2....1...-2....2....0....0....0...-1....0....0...-2...-1...-2....2....2....0

%e .-2....0....2....0....2...-1...-1...-2....1....1....0....0...-1....0...-2....1

%e ..0....1....1...-1...-2...-2...-2....2....0....2....1....2....0...-1...-1...-1

%e .-1....0...-1....0...-1....0....2...-2...-1...-2....0....0....2....0...-2....0

%e ..0...-2....0...-2....0....2....0....2....1....0....2...-1....1....1....2....1

%K nonn

%O 1,2

%A _R. H. Hardin_ Nov 11 2011