OFFSET
1,2
COMMENTS
Row 3 of A221087.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..34
FORMULA
Empirical: a(n) = 24*a(n-1) - 648*a(n-3) + 729*a(n-4) for n>7.
Empirical g.f.: x^2*(16 - 114*x + 409*x^2 - 528*x^3 - 5103*x^4 + 6480*x^5) / ((1 - 24*x + 27*x^2)*(1 - 27*x^2)). - Colin Barker, Aug 03 2018
EXAMPLE
Some solutions for n=3:
..1..2..0....0..1..0....0..1..0....0..2..0....1..1..0....0..1..1....1..2..0
..0..2..0....1..2..2....1..3..1....2..2..1....0..4..1....0..4..0....0..2..0
..2..2..0....0..3..0....1..2..0....0..2..0....1..1..0....2..1..0....1..2..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 01 2013
STATUS
approved