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 0's, every 3 is next to 3 1's, every 4 is next to 4 4's.
Column 2 of A196590.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +6*a(n-2) +4*a(n-3) -3*a(n-4) -a(n-5) -2*a(n-6) -a(n-7).
Empirical g.f.: x*(1 + 6*x + 7*x^2 - x^3 - 7*x^4 - 3*x^5) / (1 - x - 6*x^2 - 4*x^3 + 3*x^4 + x^5 + 2*x^6 + x^7). - Colin Barker, Feb 22 2018
EXAMPLE
Some solutions for n=4:
..0..0....0..0....0..2....0..0....0..1....2..0....2..0....0..0....0..2....0..0
..0..0....2..2....0..0....0..2....0..2....0..1....0..2....0..0....2..0....2..2
..2..2....0..0....0..0....0..1....0..0....0..2....0..1....0..0....1..0....0..0
..0..0....0..0....2..0....2..0....0..2....0..0....0..0....0..0....0..0....2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 04 2011
STATUS
approved