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 0's, every 3 is next to 3 2's, every 4 is next to 4 4's.
Column 2 of A196322.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +2*a(n-2) +2*a(n-3) -a(n-5).
Empirical g.f.: x*(1 + 6*x + x^2 - 3*x^3) / ((1 + x + x^2)*(1 - 2*x - x^2 + x^3)). - Colin Barker, Feb 18 2018
EXAMPLE
Some solutions for n=4:
..0..0....2..0....0..2....0..0....0..2....0..0....0..0....0..2....0..0....0..2
..0..2....0..2....2..0....0..0....0..0....0..0....0..2....0..0....2..2....0..0
..0..2....0..2....2..0....0..0....0..0....0..0....0..2....0..0....0..0....0..0
..2..0....0..0....0..2....0..2....0..2....2..0....0..0....0..0....2..0....2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 01 2011
STATUS
approved