OFFSET
2,1
LINKS
R. H. Hardin, Table of n, a(n) for n=2..99
FORMULA
Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>=7.
Conjectures from Colin Barker, Mar 26 2018: (Start)
G.f.: x^2*(33 - 5*x - 25*x^2 + 18*x^3 - 3*x^4) / (1 - x)^3.
a(n) = 9*n^2 + 4*n - 2 for n>3.
(End)
EXAMPLE
Some solutions for n=4:
...1.1.2.2.........1.1.2.2.........1.1.1.2.........1.1.2.2......
.....1.1.3.4.........1.1.4.4.........3.3.2.2.........1.1.2.2....
.......1.3.4.4.........1.3.4.4.........3.3.2.2.........3.3.4.4..
.........3.3.4.4.........3.3.4.4.........3.3.3.4.........3.3.4.4
------
...1.1.2.2.........1.1.2.2.........1.2.2.2.........1.1.2.2......
.....1.3.2.2.........3.3.2.2.........3.3.2.2.........1.3.2.2....
.......3.3.4.4.........3.3.4.4.........3.3.2.2.........3.3.2.3..
.........3.3.4.4.........3.3.4.4.........3.3.3.4.........3.3.3.4
------
...1.1.2.2.........1.1.2.2.........1.1.2.2.........1.3.2.2......
.....1.1.1.4.........1.1.2.2.........1.2.4.4.........3.3.2.2....
.......3.3.4.4.........1.3.4.4.........2.2.4.4.........3.3.2.3..
.........3.3.4.4.........3.3.4.4.........3.3.4.4.........3.3.3.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved