OFFSET
1,3
COMMENTS
Every 0 is next to 0 0's, every 1 is next to 1 3'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 A197623.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-2) +4*a(n-3) +a(n-4).
Empirical g.f.: 8*x^3 / (1 - x^2 - 4*x^3 - x^4). - Colin Barker, May 14 2018
EXAMPLE
All solutions for n=5:
..0..1....1..0....1..2....1..0....1..2....2..1....2..1....0..1
..1..3....3..1....3..1....3..1....3..1....1..3....1..3....1..3
..1..1....1..1....1..1....1..1....1..1....1..1....1..1....1..1
..3..1....1..3....1..3....1..3....1..3....3..1....3..1....3..1
..1..0....0..1....0..1....2..1....2..1....1..0....1..2....1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 16 2011
STATUS
approved