OFFSET
1,4
COMMENTS
Column 1 of A209610.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) - a(n-2) + a(n-6).
Empirical g.f.: x*(1 - x + x^2 - x^3 + 2*x^4) / ((1 - x + x^3)*(1 - x - x^3)). - Colin Barker, Jul 11 2018
EXAMPLE
All solutions for n=9:
..2....2....1....1....1....2....1....1....1....2....2....1....1
..2....2....1....1....1....2....1....1....1....2....2....1....1
..2....2....2....1....1....2....1....2....1....2....2....1....2
..2....2....2....1....2....2....2....2....1....2....2....1....2
..1....2....2....1....2....2....2....2....1....2....2....2....2
..1....2....2....2....2....2....2....2....1....2....1....2....2
..1....1....2....2....2....2....2....2....1....2....1....2....1
..1....1....1....2....2....1....1....2....1....2....1....2....1
..1....1....1....2....2....1....1....2....1....2....1....2....1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 10 2012
STATUS
approved