OFFSET
1,1
COMMENTS
Column 2 of A203371.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) +5*a(n-2) +2*a(n-3) +a(n-4).
Empirical g.f.: x*(2 + 5*x + 2*x^2 + x^3) / (1 - 2*x - 5*x^2 - 2*x^3 - x^4). - Colin Barker, Jun 04 2018
EXAMPLE
Some solutions for n=4:
..0..1....0..0....0..0....0..0....0..1....0..0....0..1....0..1....0..0....0..0
..1..0....0..0....0..0....0..0....0..2....0..0....0..1....0..1....0..0....1..1
..0..0....1..0....1..2....0..0....1..0....0..0....0..0....0..2....0..1....0..0
..1..2....0..0....0..0....0..1....0..1....0..0....0..1....0..0....0..0....0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 31 2011
STATUS
approved