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 4's, every 4 is next to 4 0's.
Column 3 of A196922.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 2*a(n-1) +a(n-3) -a(n-4) for n>5.
Empirical g.f.: x*(1 + x + x^2 - 3*x^3 + x^4) / (1 - 2*x - x^3 + x^4). - Colin Barker, May 09 2018
EXAMPLE
Some solutions for n=4:
..0..0..0....0..2..2....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0
..2..2..2....0..2..2....0..0..0....2..2..0....0..0..0....0..0..0....0..0..0
..2..0..2....0..0..0....0..2..2....2..2..0....2..2..0....0..4..0....0..0..0
..2..2..2....0..0..0....0..2..2....0..0..0....2..2..0....0..0..0....0..0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 07 2011
STATUS
approved