OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 5*a(n-1) - 2*a(n-2) - 12*a(n-3).
Conjectures from Colin Barker, Jan 11 2019: (Start)
G.f.: x*(1 - x - 3*x^2) / ((1 - 3*x)*(1 - 2*x - 4*x^2)).
a(n) = -3^n + (5/8-11/(8*sqrt(5)))*(1-sqrt(5))^n + (1/40)*(1+sqrt(5))^n*(25+11*sqrt(5)).
(End)
EXAMPLE
Some solutions for n=6:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..1....3....0....1....3....1....1....0....1....2....3....2....3....2....1....1
..2....0....1....0....2....1....0....1....3....1....2....3....3....3....1....0
..1....2....3....0....1....0....1....2....1....2....2....1....0....1....2....2
..3....0....1....2....3....3....2....1....3....2....1....3....2....1....2....1
..1....3....3....1....2....2....1....1....1....3....0....0....0....2....1....0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 27 2016
STATUS
approved