OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3); a(n) = (180*3^n - 80*2^n + 26)/2.
Empirical g.f.: x*(7 - 9*x)*(29 - 42*x) / ((1 - x)*(1 - 2*x)*(1 - 3*x)). - Colin Barker, Nov 17 2018
EXAMPLE
Some solutions for n=4:
..2..2..2..2..2....2..2..2..2..2....1..1..1..1..1....0..0..0..0..0
..2..2..2..2..2....1..1..1..1..1....1..1..1..1..1....0..0..0..0..0
..1..1..1..1..1....0..1..1..1..1....1..2..2..2..2....0..0..0..0..0
..0..0..0..0..0....1..2..2..2..2....0..1..1..1..1....1..1..1..1..2
..0..0..0..1..2....0..1..2..2..2....0..1..1..1..2....1..1..1..1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 27 2014
STATUS
approved