OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = (1/5040)*n^7 + (7/720)*n^6 + (29/144)*n^5 + (305/144)*n^4 + (1027/45)*n^3 + (16267/180)*n^2 + (2425/21)*n + 24 for n>1.
Empirical g.f.: x*(256 - 1208*x + 2476*x^2 - 2856*x^3 + 2026*x^4 - 904*x^5 + 242*x^6 - 32*x^7 + x^8) / (1 - x)^8. - Colin Barker, Jan 26 2018
EXAMPLE
Some solutions for n=4:
..3....0....0....2....3....1....1....1....1....0....0....0....3....2....0....0
..0....3....0....2....2....0....3....1....1....0....0....2....2....1....1....2
..0....3....2....2....2....1....2....2....1....0....0....2....2....2....1....3
..1....3....2....0....2....1....2....3....2....2....1....2....2....3....1....3
..2....1....0....1....3....1....2....3....0....2....1....3....2....3....0....3
..2....1....0....1....0....2....2....3....0....0....1....0....0....0....2....1
..2....3....2....3....1....2....0....1....1....0....3....2....3....3....3....2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 08 2015
STATUS
approved