OFFSET
1,2
COMMENTS
Column 2 of A198906.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..200
FORMULA
Empirical: a(n) = 17*a(n-1) -55*a(n-2) +39*a(n-3).
Conjectures from Colin Barker, Feb 18 2018: (Start)
G.f.: x*(1 - 13*x + 20*x^2) / ((1 - x)*(1 - 3*x)*(1 - 13*x)).
a(n) = (26 + 13*3^n + 13^n) / 78.
(End)
EXAMPLE
Some solutions with values 0 to 4 for n=4:
..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..2..3....2..3....2..0....1..2....1..0....2..3....2..3....2..3....1..2....2..3
..4..2....1..4....3..2....3..1....2..3....1..4....3..1....4..2....2..3....4..0
..2..4....3..2....4..3....2..4....4..2....4..3....4..2....2..0....4..0....0..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 31 2011
STATUS
approved