OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 42*a(n-1) - 441*a(n-2).
Conjectures from Colin Barker, Jan 21 2019: (Start)
G.f.: 12*x*(5 - 33*x) / (1 - 21*x)^2.
a(n) = 4 * 3^n * 7^(n-2) * (24*n+11).
(End)
EXAMPLE
Some solutions for n=3:
..2..0..0. .0..1..3. .0..2..3. .2..0..2. .2..2..3. .3..0..1. .3..1..0
..0..2..0. .3..1..2. .3..3..3. .1..0..0. .0..1..0. .1..3..2. .1..1..0
..1..1..0. .1..0..0. .2..3..3. .0..1..3. .1..0..2. .2..0..1. .3..0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 21 2016
STATUS
approved