OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - 2*a(n-3) - 2*a(n-4).
Empirical g.f.: 2*x*(1 + 4*x - 4*x^2 - 3*x^3) / (1 - 2*x - 2*x^2 + 2*x^3 + 2*x^4). - Colin Barker, Jan 09 2019
EXAMPLE
Some solutions for n=4:
..0..3..1....1..0..2....1..0..2....1..1..2....1..0..1....1..0..1....1..1..2
..1..0..2....2..1..2....2..0..2....2..0..2....1..4..1....1..4..0....2..0..2
..2..0..2....0..1..2....2..0..2....2..0..1....1..0..2....0..4..1....2..0..2
..2..0..1....2..1..1....2..1..0....1..3..0....2..1..0....1..0..1....2..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 20 2015
STATUS
approved