OFFSET
1,2
COMMENTS
Every 0 is next to 0 3's, every 1 is next to 1 2's, every 2 is next to 2 1's, every 3 is next to 3 0's, every 4 is next to 4 4's.
Column 2 of A196982.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 2*a(n-1) + a(n-2) + 4*a(n-3) - 2*a(n-4) - a(n-6).
Empirical g.f.: x*(1 + x)^2*(1 + x - x^3) / (1 - 2*x - x^2 - 4*x^3 + 2*x^4 + x^6). - Colin Barker, Mar 01 2018
EXAMPLE
Some solutions for n=4:
..0..0....1..2....1..0....0..0....0..0....0..0....0..1....0..1....1..1....1..0
..0..0....0..1....2..0....0..0....1..0....1..2....0..2....1..2....2..2....2..1
..1..0....2..1....1..1....0..1....2..1....0..1....1..1....1..0....1..1....0..1
..2..1....1..0....1..2....1..2....0..0....0..0....2..1....2..1....0..0....1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 08 2011
STATUS
approved