

A268093


Number of 1 X n 0..2 arrays with every repeated value in every row not one larger and in every column one larger mod 3 than the previous repeated value, and upper left element zero.


1



1, 3, 9, 26, 74, 208, 580, 1608, 4440, 12224, 33584, 92128, 252448, 691200, 1891392, 5173376, 14145920, 38671360, 105700096, 288873984, 789410304, 2157092864, 5894054912, 16104392704, 44001089536, 120219353088, 328457662464
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OFFSET

1,2


LINKS



FORMULA

Empirical: a(n) = 4*a(n1)  2*a(n2)  4*a(n3).
G.f.: x*(1  x  x^2) / ((1  2*x)*(1  2*x  2*x^2)).
a(n) = (3*2^n + (32*sqrt(3))*(1sqrt(3))^n + (1+sqrt(3))^n*(3+2*sqrt(3))) / 12.
(End)


EXAMPLE

Some solutions for n=4:
..0..2..2..1....0..2..1..0....0..0..1..2....0..0..2..2....0..0..2..0


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



