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%I #9 May 14 2018 10:39:38
%S 5,193,10072,528283,27711478,1453628917,76251331828,3999827976463,
%T 209814352850962,11005988987858473,577328442763429648,
%U 30284250801208664707,1588585939401430092718,83330616412779323165533
%N Number of 2n X 2 0..3 arrays with values 0..3 introduced in row major order and each element equal to an even number of horizontal and vertical neighbors.
%C Column 1 of A198485.
%H R. H. Hardin, <a href="/A198482/b198482.txt">Table of n, a(n) for n = 1..200</a>
%F Empirical: a(n) = 55*a(n-1) -135*a(n-2) +81*a(n-3) for n>4.
%F Empirical g.f.: x*(5 - 82*x + 132*x^2 - 27*x^3) / ((1 - x)*(1 - 54*x + 81*x^2)). - _Colin Barker_, May 14 2018
%e Some solutions for n=3:
%e ..0..1....0..0....0..1....0..1....0..1....0..1....0..0....0..1....0..1....0..1
%e ..2..3....0..0....2..3....2..3....1..0....2..2....0..0....2..0....1..2....2..0
%e ..1..1....1..2....0..2....1..2....2..1....2..2....1..2....1..2....3..0....0..3
%e ..1..1....2..0....2..1....2..1....1..3....3..1....3..0....0..3....0..2....1..0
%e ..3..2....0..3....1..2....1..0....0..1....2..0....2..2....1..0....1..3....0..1
%e ..2..0....2..0....3..0....2..1....1..0....3..1....2..2....2..3....3..0....1..3
%Y Cf. A198485.
%K nonn
%O 1,1
%A _R. H. Hardin_, Oct 25 2011