OFFSET
2,1
COMMENTS
Same recurrence for A165392.
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>=9.
Conjectures from Colin Barker, Feb 26 2018: (Start)
G.f.: x^2*(37 + 174*x + 268*x^2 + 249*x^3 + 58*x^4 + 13*x^5 + x^6) / (1 - x)^3.
a(n) = 4*(817 - 540*n + 100*n^2) for n>5.
(End)
EXAMPLE
Some solutions for n=3:
...1.3.2.2.......1.1.3.2.......1.1.1.2.......1.1.2.2.......1.1.2.2....
.....3.3.2.2.......3.3.2.2.......1.4.4.4.......1.2.2.2.......1.3.2.2..
.......3.3.3.4.......3.3.3.4.......3.4.4.4.......3.3.3.4.......3.2.2.4
------
...1.1.2.2.......1.1.2.2.......1.1.1.2.......1.1.2.2.......1.1.1.2....
.....1.1.1.4.......2.2.2.4.......2.2.2.4.......2.2.4.4.......1.1.2.4..
.......3.1.4.4.......3.4.4.4.......3.4.4.4.......3.4.4.4.......3.3.4.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved