OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + a(n-2) - a(n-3) + a(n-4) for n>12.
Empirical g.f.: x*(1 + x + 3*x^2 + 7*x^3 - 5*x^4 - 8*x^5 - 2*x^7 - x^9 - 2*x^10 - x^11) / (1 - x - x^2 + x^3 - x^4). - Colin Barker, Jan 02 2019
EXAMPLE
Some solutions for n=7:
..0....0....0....1....0....1....1....0....0....0....0....1....2....0....0....0
..1....1....2....0....2....0....0....3....1....1....1....0....0....1....2....1
..2....2....1....2....1....3....2....1....2....2....3....2....1....2....1....3
..3....4....3....3....4....2....3....2....4....3....2....3....3....3....4....2
..5....3....4....4....3....5....5....4....3....4....4....4....4....4....3....5
..4....5....6....5....6....4....6....5....6....5....5....6....5....6....5....4
..6....6....5....6....5....6....4....6....5....6....6....5....6....5....6....6
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 23 2015
STATUS
approved