OFFSET
1,2
COMMENTS
Every 0 is next to 0 2's, every 1 is next to 1 2's, every 2 is next to 2 1's, every 3 is next to 3 1's, every 4 is next to 4 1's.
Column 2 of A197545.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +2*a(n-3) +4*a(n-4) -3*a(n-5) -a(n-6) +3*a(n-7) -2*a(n-8).
Empirical g.f.: x*(1 + 4*x + 3*x^2 + 9*x^3 - 5*x^4 - 3*x^5 + 7*x^6 - 6*x^7) / (1 - x - 2*x^3 - 4*x^4 + 3*x^5 + x^6 - 3*x^7 + 2*x^8). - Colin Barker, May 13 2018
EXAMPLE
Some solutions for n=4:
..2..1....1..2....2..1....1..0....0..0....2..1....1..2....1..1....1..2....2..1
..1..0....0..1....1..0....2..1....0..0....1..0....3..1....2..2....0..1....1..3
..3..1....1..0....1..0....2..1....0..1....0..1....1..3....1..1....1..3....0..1
..1..2....2..1....2..1....1..0....1..2....1..2....2..1....0..0....2..1....1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 16 2011
STATUS
approved