OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 2*a(n-2) +a(n-3).
Empirical g.f.: x*(4 + 2*x + x^2) / (1 - 4*x - 2*x^2 - x^3). - Colin Barker, Dec 20 2018
EXAMPLE
Some solutions for n=4:
..4....4....3....4....2....2....3....4....3....2....4....6....6....3....4....6
..4....2....3....2....6....2....7....2....5....4....5....4....4....3....5....2
..6....2....3....2....2....4....5....3....7....3....7....6....5....6....7....4
..2....1....6....4....6....1....3....3....7....1....6....2....7....3....4....4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 15 2015
STATUS
approved