OFFSET
2,1
LINKS
R. H. Hardin, Table of n, a(n) for n=2..99
FORMULA
Empirical: a(n) = 2*a(n-1) - a(n-2) for n>=5.
Conjectures from Colin Barker, Mar 25 2018: (Start)
G.f.: x^2*(9 + 22*x + 33*x^2) / (1 - x)^2.
a(n) = 8*(8*n-19) for n>2.
(End)
EXAMPLE
Some solutions for n=6:
...1.2.2.............1.2.2.............1.1.2.............1.1.2..........
.....2.2.2.............2.2.2.............1.2.2.............1.1.1........
.......2.2.2.............2.3.3.............2.2.2.............1.1.3......
.........2.2.2.............3.3.3.............2.2.2.............3.3.3....
...........4.4.4.............3.3.3.............2.2.2.............3.3.3..
.............3.4.4.............3.3.4.............3.3.4.............3.3.4
------
...1.1.2.............1.1.2.............1.1.2.............1.1.2..........
.....1.1.1.............1.2.2.............1.1.1.............1.1.1........
.......1.1.3.............2.2.3.............1.1.1.............1.1.1......
.........3.3.3.............3.3.3.............1.1.3.............1.1.1....
...........3.3.4.............3.3.3.............3.3.4.............3.3.3..
.............3.4.4.............3.4.4.............3.4.4.............3.3.4
------
...1.1.2.............1.1.2.............1.2.2.............1.1.2..........
.....2.2.2.............2.2.3.............2.2.2.............1.1.1........
.......2.2.2.............2.3.3.............2.3.3.............1.1.1......
.........2.2.2.............3.3.3.............3.3.3.............3.3.3....
...........2.2.4.............3.3.4.............3.3.4.............3.3.4..
.............3.4.4.............3.4.4.............3.4.4.............3.4.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved