OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + a(n-4).
Empirical g.f.: 4*x*(31 + 3*x + 7*x^2 + 15*x^3) / (1 - 2*x - x^4). - Colin Barker, Nov 06 2018
EXAMPLE
Some solutions for n=4:
..2....3....0....1....0....1....2....1....0....1....3....1....2....3....1....0
..3....1....1....1....2....0....3....1....2....1....3....3....3....1....1....0
..2....1....0....3....2....0....3....1....2....1....3....1....3....3....3....0
..2....3....0....1....2....0....3....1....2....1....1....3....3....3....3....0
..2....3....1....3....0....1....3....1....0....1....3....1....3....3....3....2
..2....3....1....3....0....0....2....1....2....3....1....1....3....3....3....0
..2....1....1....3....2....0....3....1....2....1....3....1....1....3....1....2
..0....1....1....3....2....0....2....0....2....3....1....3....1....1....1....2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 02 2014
STATUS
approved