OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) + 9*a(n-2).
Conjectures from Colin Barker, Sep 26 2018: (Start)
G.f.: 6*x^2 / ((1 + x)*(1 - 9*x)).
a(n) = (9^n + 9) / 15 for n even.
a(n) = (9^n - 9) / 15 for n odd.
(End)
EXAMPLE
Some solutions for n=4:
..0..1..2..1....0..1..2..3....0..1..2..1....0..1..0..1....0..1..2..3
..0..3..0..2....2..3..0..3....0..3..2..1....2..3..2..1....0..3..0..1
..1..2..3..0....0..1..2..3....2..1..0..3....2..3..0..1....2..3..2..3
..1..2..1..0....0..1..0..3....2..3..2..1....2..3..2..1....2..1..0..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 03 2013
STATUS
approved