OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 19*a(n-1) - 45*a(n-2) + 27*a(n-3).
Empirical g.f.: x*(5 - 21*x + 21*x^2) / ((1 - x)*(1 - 18*x + 27*x^2)). - Colin Barker, Oct 06 2018
EXAMPLE
Some solutions for n=4:
..0..1..1....0..1..3....0..1..1....0..1..1....0..1..3....0..0..1....0..1..0
..1..1..1....0..0..2....2..0..1....2..0..0....1..3..1....0..0..0....1..1..1
..3..1..1....2..2..2....3..2..3....2..2..0....3..1..0....0..0..1....3..3..3
..2..0..0....2..3..2....1..3..3....0..0..2....3..1..1....0..0..1....1..1..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 03 2013
STATUS
approved