OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 6*a(n-3) - 6*a(n-4) - 8*a(n-6) + 8*a(n-7) for n>12.
Empirical g.f.: 2*x*(640 - 339*x - 23*x^2 - 3729*x^3 + 2275*x^4 + 326*x^5 + 4875*x^6 - 3427*x^7 - 303*x^8 - 28*x^9 + 220*x^10 - 484*x^11) / ((1 - x)*(1 - 2*x^3)*(1 - 4*x^3)). - Colin Barker, Nov 30 2018
EXAMPLE
Some solutions for n=4:
..0..0..1..0..0....2..3..0..1..0....3..3..2..3..0....2..1..1..2..1
..0..0..1..0..0....1..0..0..1..0....3..3..2..3..3....1..0..0..1..0
..1..1..3..1..1....2..1..1..3..1....2..2..0..2..2....1..0..0..1..0
..0..0..1..0..0....1..0..0..1..0....3..3..2..3..3....2..1..1..3..1
..3..0..1..0..3....1..0..0..1..0....3..3..2..3..0....1..0..0..1..3
..1..1..2..1..1....3..1..1..2..1....2..2..0..2..2....1..0..0..1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 10 2014
STATUS
approved