OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 5*a(n-2).
Conjectures from Colin Barker, Sep 26 2018: (Start)
G.f.: 2*x^2 / ((1 + x)*(1 - 5*x)).
a(n) = (5^n + 5) / 15 for n even.
a(n) = (5^n - 5) / 15 for n odd.
(End)
EXAMPLE
Some solutions for n=4:
..0..1..0....0..1..2....0..1..0....0..1..2....0..1..2....0..1..2....0..1..2
..2..3..1....0..3..0....2..3..0....2..3..0....0..3..2....0..3..2....0..3..1
..1..2..1....2..1..0....0..1..0....0..1..0....2..0..3....2..3..2....1..2..3
..3..0..3....0..3..2....2..3..2....2..3..2....1..2..1....0..1..0....1..0..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 03 2013
STATUS
approved