OFFSET
1,3
COMMENTS
Every 0 is next to 0 2's, every 1 is next to 1 3's, every 2 is next to 2 1's, every 3 is next to 3 1's, every 4 is next to 4 0's.
Column 2 of A197503.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +a(n-2) +2*a(n-3) -a(n-4).
Empirical g.f.: x*(1 + 7*x^2 - 3*x^3) / (1 - x - x^2 - 2*x^3 + x^4). - Colin Barker, May 12 2018
EXAMPLE
All solutions for n=4:
..0..0....2..1....0..0....0..0....1..0....0..0....1..2....0..1....0..0
..0..1....1..3....0..1....0..0....3..1....1..0....3..1....1..3....1..0
..1..3....0..1....1..3....0..0....1..0....3..1....1..0....0..1....3..1
..2..1....0..0....0..1....0..0....0..0....1..2....0..0....0..0....1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 15 2011
STATUS
approved