OFFSET
1,2
COMMENTS
Column 1 of A201625.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = (1/6)*n^3 - n^2 + (35/6)*n - 9 for n>4.
For n > 4 the above empirical a(n) is equal to C(n-1,3) + 4C(n-2,1) that is the n-th coefficient in Taylor series of ((1-x+x^2)/(1-x))^4 at x=0. - Nikita Gogin, Jul 24 2013
Conjectures from Colin Barker, May 23 2018: (Start)
G.f.: x^2*(2 - 2*x + x^2)*(2 - 4*x + 4*x^2 - 2*x^3 + x^4) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>8.
(End)
EXAMPLE
Some solutions for n=10:
..1....0....0....2....1....1....1....0....0....0....0....1....2....0....0....0
..1....0....0....2....1....1....1....0....0....0....0....1....2....0....0....0
..1....0....2....2....1....1....1....0....0....1....1....1....3....0....1....0
..1....1....2....2....1....2....1....0....0....1....1....2....3....0....1....0
..2....1....3....2....1....2....1....0....1....3....1....2....3....0....2....2
..2....2....3....2....1....2....1....0....1....3....1....2....3....3....2....2
..2....2....3....2....1....3....2....2....1....3....1....2....3....3....3....2
..2....2....3....2....1....3....2....2....2....3....1....2....3....3....3....2
..2....3....3....3....2....3....3....2....2....3....1....2....3....3....3....2
..2....3....3....3....2....3....3....2....2....3....1....2....3....3....3....2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 03 2011
STATUS
approved