OFFSET
1,2
COMMENTS
Every 0 is next to 0 0'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 0's.
Column 2 of A198185.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 3*a(n-2) +2*a(n-3) -2*a(n-4) -2*a(n-5) +4*a(n-7) -a(n-8) -3*a(n-9).
Empirical g.f.: x^2*(4 + 3*x - 4*x^2 - x^3 - x^4 + 6*x^5 - 3*x^6 - 7*x^7) / ((1 - x)*(1 + x - 2*x^2 - 4*x^3 - 2*x^4 - 4*x^7 - 3*x^8)). - Colin Barker, May 14 2018
EXAMPLE
All solutions for n=4:
..1..2....2..1....1..0....0..1....1..2....1..0....0..1....2..1
..0..1....1..0....2..1....1..2....0..1....2..1....1..2....1..0
..2..1....0..1....0..1....1..0....1..0....2..1....1..2....1..2
..1..0....1..2....1..2....2..1....2..1....1..0....0..1....0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 21 2011
STATUS
approved