OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) - 13*a(n-2) + 12*a(n-3) - 4*a(n-4) for n>7.
Empirical g.f.: 2*x*(10 + 48*x - 337*x^2 + 482*x^3 - 145*x^4 - 32*x^5 + 20*x^6) / ((1 - x)^2*(1 - 2*x)^2). - Colin Barker, Sep 19 2018
EXAMPLE
Some solutions for n=3:
..0..1..2..3..2....0..1..0..1..2....0..1..2..3..0....0..1..0..2..3
..2..3..0..1..0....2..1..2..3..0....2..3..0..1..2....3..2..3..1..1
..1..0..2..3..2....0..3..0..1..2....2..1..2..3..0....0..1..0..2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 26 2013
STATUS
approved