OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 17*a(n-2).
Conjectures from Colin Barker, Sep 28 2018: (Start)
G.f.: 2*x^2 / (1 - 4*x - 17*x^2).
a(n) = ((2-sqrt(21))^n*(2+sqrt(21)) + (-2+sqrt(21))*(2+sqrt(21))^n)/(17*sqrt(21)).
(End)
EXAMPLE
Some solutions for n=3:
..0..1..0....0..1..2....0..1..0....0..1..2....0..1..2....0..1..2....0..1..0
..2..3..2....0..3..0....2..3..0....2..3..0....0..3..2....2..3..2....2..3..2
..0..1..0....2..1..0....2..1..0....2..1..0....2..1..0....0..1..0....2..1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 06 2013
STATUS
approved