OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 127*a(n-1) - 2331*a(n-2) + 2205*a(n-3).
Conjectures from Colin Barker, Oct 10 2018: (Start)
G.f.: 2*x*(3 - 193*x + 840*x^2) / ((1 - x)*(1 - 21*x)*(1 - 105*x)).
a(n) = (105 + 2*3^(2+n)*7^n + 5^(1+n)*21^n) / 168.
(End)
EXAMPLE
Some solutions for n=3:
..0..1..5....0..1..0....0..1..5....0..0..1....0..1..2....0..1..2....0..0..1
..5..2..2....2..2..0....1..2..1....1..2..1....5..1..2....2..2..2....2..0..1
..1..2..1....1..2..5....5..5..5....4..2..2....0..0..3....2..4..5....1..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 06 2013
STATUS
approved