OFFSET
1,4
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..50
FORMULA
Empirical: a(n) = 36*n^2 - 260*n + 440 for n>5.
G.f.: 8*x^4*(1 + 3*x + 7*x^2 - x^3 - x^4) / (1 - x)^3 (conjectured). - Colin Barker, Apr 22 2018
EXAMPLE
Some solutions for 4 X 4:
..0..0..1..0....0..0..3..0....0..0..4..0....0..0..2..0....0..0..1..0
..4..0..0..0....4..0..0..0....3..0..0..0....1..0..0..0....2..0..0..0
..0..0..0..2....0..0..0..2....0..0..0..1....0..0..0..3....0..0..0..4
..0..3..0..0....0..1..0..0....0..2..0..0....0..4..0..0....0..3..0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 06 2011
STATUS
approved