OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + a(n-2) + a(n-3).
Empirical g.f.: 4*x / (1 - x - x^2 - x^3). - Colin Barker, Oct 05 2018
EXAMPLE
Some solutions for n=7:
..1..0....0..1....1..0....1..0....0..1....2..1....0..1....1..0....0..1....0..1
..1..2....2..1....1..2....1..2....2..1....0..1....2..1....1..2....2..1....2..1
..1..0....2..1....1..0....1..0....2..0....0..1....2..1....1..2....0..1....0..1
..1..2....0..1....1..2....1..2....1..0....2..1....0..1....1..0....2..1....0..2
..1..0....2..1....1..0....1..2....1..2....0..1....0..1....1..0....2..1....1..2
..1..2....0..1....1..2....1..0....1..2....0..1....2..1....1..2....0..1....1..0
..1..2....0..1....1..0....1..0....1..0....2..1....0..1....1..0....2..1....1..0
..1..0....2..1....1..2....1..2....1..2....0..1....2..1....1..2....0..1....1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 25 2013
STATUS
approved