OFFSET
1,1
LINKS
R. H. Hardin,Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 12*a(n-1) - 38*a(n-2) + 12*a(n-3) - a(n-4) for n>5.
Empirical g.f.: 4*x*(1 - x)*(1 + 9*x - x^2 - x^3) / (1 - 6*x + x^2)^2. -Colin Barker,Jan 19 2019
EXAMPLE
Some solutions for n=4:
..3..2..0..0..2..0..3..3..1..0..1..0..1..3..3..1..0..2..1..1
..2..0..2..3..0..2..3..3..1..1..0..2..0..1..1..0..0..0..3..3
..1..0..2..2..0..3..1..0..1..3..0..0..0..0..0..1..2..3..3..2
..0..1..3..3..2..3..0..0..1..0..1..3..2..0..0..2..3..3..0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin,Feb 20 2016
STATUS
approved