OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 5*a(n-2) - 4*a(n-4).
Conjectures from Colin Barker, Oct 25 2018: (Start)
G.f.: x*(1 + 3*x - x^2 - 4*x^3) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 + 2*x)).
a(n) = (2 + (-2)^n + 2*(-1)^n + 7*2^n) / 12.
(End)
EXAMPLE
Some solutions for n=5:
..2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0
..1..0....2..0....2..0....2..0....1..2....1..0....1..0....2..0....2..0....1..0
..2..0....1..2....1..0....1..2....2..1....2..0....2..0....1..2....1..2....2..0
..2..0....2..1....1..0....1..2....1..0....1..0....1..2....2..1....1..2....2..0
..1..2....1..2....2..0....2..1....2..0....2..0....2..1....1..0....2..0....1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2014
STATUS
approved