OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 7*a(n-1) - 4*a(n-2).
Conjectures from Colin Barker, Oct 16 2018: (Start)
G.f.: 4*x*(19 - 12*x) / (1 - 7*x + 4*x^2).
a(n) = (2^(1-n)*((7-sqrt(33))^n*(-17+3*sqrt(33)) + (7+sqrt(33))^n*(17+3*sqrt(33)))) / sqrt(33).
(End)
EXAMPLE
Some solutions for n=5:
..3..2....2..0....1..0....2..3....3..2....3..2....1..0....1..2....2..0....2..1
..2..1....0..3....0..1....1..2....2..1....2..1....2..1....2..0....1..3....0..2
..0..2....2..1....2..3....3..0....1..3....0..3....0..3....1..3....3..1....1..3
..2..0....1..3....0..1....2..3....2..0....3..0....3..2....2..0....1..3....0..1
..0..3....0..1....2..3....0..1....0..1....0..2....0..3....3..2....0..1....1..3
..3..0....3..0....3..2....1..0....3..0....1..3....3..0....2..1....1..3....2..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 30 2013
STATUS
approved