OFFSET
1,1
COMMENTS
Column 2 of A230935.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) - a(n-2) + 3*a(n-3).
Empirical g.f.: 2*x / ((1 - 3*x)*(1 + x^2)). - Colin Barker, Mar 17 2018
EXAMPLE
Some solutions for n=4:
..x..0..x..2....x..0..x..0....x..0..x..2....x..0..x..2....x..0..x..0
..1..x..3..x....3..x..1..x....1..x..3..x....1..x..3..x....1..x..1..x
..x..2..x..2....x..2..x..3....x..2..x..0....x..2..x..2....x..2..x..2
..1..x..3..x....0..x..0..x....3..x..1..x....3..x..3..x....3..x..3..x
..x..0..x..2....x..1..x..3....x..0..x..0....x..0..x..2....x..0..x..2
..3..x..1..x....0..x..2..x....3..x..3..x....3..x..1..x....3..x..1..x
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 01 2013
STATUS
approved