OFFSET
1,1
COMMENTS
Every 0 is next to 0 3's, every 1 is next to 1 1'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 A196912.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) + 2*a(n-2) + 3*a(n-3) + 2*a(n-4) - a(n-6).
Empirical g.f.: x*(2 + 4*x + 3*x^2 + 3*x^3 - x^4 - x^5) / (1 - x - 2*x^2 - 3*x^3 - 2*x^4 + x^6). - Colin Barker, Mar 01 2018
EXAMPLE
Some solutions for n=4:
..1..1....1..1....0..1....1..1....2..2....1..1....0..0....1..1....1..1....2..2
..0..0....0..0....0..1....0..0....2..2....0..0....2..2....0..0....2..2....2..2
..1..0....0..0....0..0....0..1....0..1....1..1....2..2....2..2....2..2....0..0
..1..0....0..0....0..0....0..1....0..1....0..0....0..0....2..2....0..0....1..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 07 2011
STATUS
approved