OFFSET
1,3
COMMENTS
Every 0 is next to 0 0's, every 1 is next to 1 1'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 A197317.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = a(n-1) +6*a(n-2) -6*a(n-3) -9*a(n-4) +10*a(n-5) -3*a(n-7).
Empirical g.f.: x*(1 - x - 3*x^2 + 5*x^3 - 2*x^4 - 7*x^5 + 6*x^6) / ((1 - 3*x^2)*(1 - x - 3*x^2 + 3*x^3 - x^5)). - Colin Barker, May 12 2018
EXAMPLE
All solutions for n=4:
..1..0....0..1
..1..2....2..1
..2..1....1..2
..0..1....1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 13 2011
STATUS
approved