OFFSET
1,1
COMMENTS
Column 2 of A209374.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + a(n-2) + 3*a(n-3) + a(n-4) - a(n-5) - a(n-6) for n>11.
Empirical g.f.: x*(8 + 31*x + 37*x^2 - 18*x^3 - 160*x^4 - 252*x^5 - 218*x^6 - 32*x^7 + 93*x^8 + 73*x^9 + 16*x^10) / ((1 + x^2 - x^3)*(1 - x - 2*x^2 - x^3)). - Colin Barker, Jul 09 2018
EXAMPLE
Some solutions for n=5:
..3..2....3..1....3..1....3..2....2..3....2..1....2..2....2..1....2..3....3..1
..1..2....2..3....1..2....1..3....2..1....1..3....1..3....2..3....2..1....1..3
..3..1....2..1....3..1....3..1....1..3....3..3....3..1....3..3....1..3....2..1
..1..3....1..3....1..3....2..3....3..2....1..3....1..3....1..3....3..1....1..3
..2..1....3..1....2..1....2..1....1..2....2..2....2..1....2..1....1..2....3..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 07 2012
STATUS
approved