OFFSET
1,2
COMMENTS
Every 0 is next to 0 1's, every 1 is next to 1 3's, every 2 is next to 2 2's, every 3 is next to 3 0's, every 4 is next to 4 4's.
Column 2 of A196636.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 2*a(n-1) + a(n-2) + a(n-3) - a(n-4).
Empirical g.f.: x*(1 - 3*x^3) / (1 - 2*x - x^2 - x^3 + x^4). - Colin Barker, Feb 22 2018
EXAMPLE
All solutions for n=4:
..0..0....0..0....0..0....0..0....0..0....0..0....2..2....0..0....0..0....0..0
..3..0....0..3....3..0....0..0....0..0....0..0....2..2....0..3....0..0....2..2
..0..0....0..0....0..3....3..0....2..2....0..3....0..0....3..0....0..0....2..2
..0..0....0..0....0..0....0..0....2..2....0..0....0..0....0..0....0..0....0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 04 2011
STATUS
approved