OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) + 6*a(n-3) + 2*a(n-4) - 2*a(n-5) - a(n-6).
Empirical g.f.: x*(4 + 9*x + 14*x^2 + 2*x^3 - 5*x^4 - 2*x^5) / (1 - 2*x - 2*x^2 - 6*x^3 - 2*x^4 + 2*x^5 + x^6). - Colin Barker, Jan 06 2019
EXAMPLE
Some solutions for n=4:
..0..1..4..2..9....5..6..1..2..9....0..3..1..2..4....5..1..4..2..3
..5..6..7..3..8....0..8..7..3..4....5..8..6..7..9....0..6..7..8..9
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 08 2015
STATUS
approved