OFFSET
1,1
COMMENTS
Every 0 is next to 0 0's, every 1 is next to 1 0'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 A197250.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 4*a(n-2) +2*a(n-3) +a(n-4) -2*a(n-5).
Empirical g.f.: 2*x*(1 - x)*(1 + x)^3 / (1 - 4*x^2 - 2*x^3 - x^4 + 2*x^5). - Colin Barker, May 11 2018
EXAMPLE
Some solutions for n=4:
..1..0....1..0....1..2....2..1....0..1....1..2....1..0....1..0....2..1....2..1
..1..2....2..1....0..1....1..0....1..3....0..1....3..1....2..1....1..0....1..0
..0..1....0..1....1..2....1..2....3..1....1..1....1..3....2..1....1..1....2..1
..1..2....1..2....1..0....0..1....1..0....1..0....0..1....1..0....0..1....0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 12 2011
STATUS
approved