OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 4*a(n-2) + 5*a(n-3) + 21*a(n-4) + 12*a(n-5) + 4*a(n-6) for n>9.
Empirical g.f.: 4*x*(73 + 194*x + 320*x^2 + 602*x^3 + 377*x^4 + 21*x^5 - 142*x^6 - 80*x^7 - 16*x^8) / (1 - x - 4*x^2 - 5*x^3 - 21*x^4 - 12*x^5 - 4*x^6). - Colin Barker, Oct 20 2018
EXAMPLE
Some solutions for n=4:
..0..0..2....2..2..1....2..2..0....1..2..2....1..0..2....2..1..1....1..1..2
..1..1..1....0..1..2....2..1..1....1..2..2....1..1..1....1..0..0....1..0..1
..1..1..2....1..0..0....1..0..1....0..1..2....1..1..0....0..0..0....2..1..1
..0..0..1....2..1..0....0..1..2....0..0..1....1..2..1....2..1..1....1..1..1
..2..1..1....1..2..2....2..2..2....2..0..1....0..1..1....1..1..1....2..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 18 2014
STATUS
approved