OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 3*a(n-3) - 3*a(n-4) - a(n-6) + a(n-7) for n>9.
Empirical g.f.: x*(616 - 257*x - 41*x^2 - 1830*x^3 + 801*x^4 + 162*x^5 + 610*x^6 - 269*x^7 - 56*x^8) / ((1 - x)*(1 - 3*x^3 + x^6)). - Colin Barker, Dec 03 2018
EXAMPLE
Some solutions for n=4:
..3..1..0..3..1..0..3..1....3..1..0..3..1..0..3..1....0..1..1..0..1..1..0..1
..3..0..1..3..0..1..3..0....3..3..3..3..3..3..3..3....2..0..0..2..0..0..2..0
..3..3..3..3..3..3..3..3....3..0..1..3..0..1..3..0....2..0..0..2..0..0..2..0
..3..1..0..3..1..0..3..1....3..1..0..3..1..0..3..1....0..1..1..0..1..1..0..1
..3..0..1..3..0..1..3..0....3..3..3..3..3..3..3..3....2..0..0..2..0..0..2..0
..3..3..3..3..3..3..3..3....3..0..1..3..0..1..3..0....2..3..3..2..3..3..2..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 16 2014
STATUS
approved