OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) - 9*a(n-3) + 3*a(n-6) - 9*a(n-7) - 9*a(n-8) + 27*a(n-9).
Empirical g.f.: x*(2 - 2*x - 7*x^2 + 4*x^3 - x^4 - 8*x^5 - 5*x^6 + 18*x^7 + 27*x^8) / ((1 - 3*x)*(1 - 3*x^2)*(1 - 3*x^6)). - Colin Barker, Jan 01 2019
EXAMPLE
Some solutions for n=4:
..3..3....0..0....3..3....0..0....3..3....3..3....0..0....1..4....3..3....0..0
..0..0....0..0....0..0....1..4....1..4....0..0....0..0....3..3....3..3....0..0
..0..0....3..3....3..3....3..3....1..4....0..0....3..3....0..0....3..3....0..0
..1..4....1..4....0..0....3..3....0..0....3..3....3..3....1..4....1..4....0..0
..1..4....1..4....3..3....1..4....0..0....0..0....0..0....3..3....1..4....0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 16 2015
STATUS
approved