OFFSET
1,2
COMMENTS
Column 1 of A211930.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..74
FORMULA
Empirical: a(n) = (1/8)*n^4 + (1/4)*n^3 - (13/8)*n^2 + (9/4)*n for n>1.
Conjectures from Colin Barker, Mar 09 2018: (Start)
G.f.: x^2*(2 - x)*(1 + 3*x^2 - x^3) / (1 - x)^5.
a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>6.
(End)
EXAMPLE
Some solutions for n=4:
..0........0........0........0........0........0........0........0
..1.2......1.2......1.0......1.2......1.2......1.2......1.2......1.2
..3.4.5....3.4.5....2.3.4....3.0.4....3.4.5....0.3.4....3.4.5....3.4.3
..6.0.7.8..6.2.7.8..5.6.7.8..5.6.7.8..6.7.8.4..5.6.7.8..6.7.8.7..5.6.7.8
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 25 2012
STATUS
approved