OFFSET
1,2
COMMENTS
Every 0 is next to 0 0's, every 1 is next to 1 1's, every 2 is next to 2 0's, every 3 is next to 3 0's, every 4 is next to 4 0's.
Column 2 of A197475.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +4*a(n-3) for n>6.
Empirical g.f.: x*(1 + x + 4*x^2 + 2*x^3 + 4*x^4 + 2*x^5) / ((1 - 2*x)*(1 + x + 2*x^2)). - Colin Barker, May 12 2018
EXAMPLE
Some solutions for n=4:
..1..1....1..1....0..1....1..1....2..0....2..0....0..2....1..0....2..0....0..2
..2..0....0..2....2..1....0..2....0..3....0..2....3..0....1..2....0..3....2..0
..0..2....3..0....0..2....2..0....3..0....2..1....0..2....2..0....2..0....1..2
..1..1....0..2....2..0....1..1....0..2....0..1....1..1....0..2....1..1....1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 15 2011
STATUS
approved