OFFSET
1,2
FORMULA
Empirical: a(n) = 4*n^4 - 10*n^3 + 6*n^2.
Empirical G.f.: 4*x^2*(2+17*x+5*x^2)/(1-x)^5. - Colin Barker, Jan 22 2012
EXAMPLE
Some solutions for 3X3
..0..0..3....0..2..3....1..0..2....0..0..3....0..3..0....0..0..0....3..2..0
..0..1..2....0..1..0....0..0..0....0..0..2....0..2..1....0..2..3....0..0..0
..0..0..0....0..0..0....0..0..3....0..0..1....0..0..0....0..1..0....0..1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 06 2011
STATUS
approved