OFFSET
2,1
LINKS
R. H. Hardin, Table of n, a(n) for n=2..48
FORMULA
Empirical: a(n) = 8*a(n-1) - 25*a(n-2) + 38*a(n-3) - 28*a(n-4) + 8*a(n-5) for n>=11.
Empirical g.f.: x^2*(105 + 782*x + 1609*x^2 + 4620*x^3 + 2932*x^4 - 3008*x^5 + 3104*x^6 + 1344*x^7 + 128*x^8) / ((1 - x)^2*(1 - 2*x)^3). - Colin Barker, Mar 26 2018
EXAMPLE
Some solutions for n=3:
...1.2.2.2.2.......1.1.1.2.2.......1.1.2.2.2.......1.1.1.2.2....
.....3.3.3.2.2.......1.1.1.2.4.......1.3.3.2.2.......1.1.1.2.2..
.......3.2.2.2.4.......3.3.2.4.4.......3.3.4.4.4.......3.1.2.4.4
------
...1.1.2.2.2.......1.1.1.2.2.......1.1.1.1.2.......1.1.2.2.2....
.....1.1.1.1.1.......1.2.2.2.2.......1.1.1.2.2.......1.1.2.2.2..
.......3.3.3.3.4.......3.3.2.4.4.......3.3.3.4.4.......3.4.4.4.4
------
...1.1.2.2.2.......1.1.1.3.2.......1.1.2.2.2.......1.1.2.2.2....
.....1.2.3.2.4.......3.3.3.2.2.......2.2.2.4.4.......2.2.2.4.4..
.......3.3.3.4.4.......3.2.2.4.4.......3.4.4.4.4.......3.2.2.4.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved