OFFSET
1,2
COMMENTS
Column 4 of A216800.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) +10*a(n-2) -28*a(n-3) -7*a(n-4) +30*a(n-5) -8*a(n-6).
Empirical g.f.: 2*x^2*(1 - 2*x)*(3 - 2*x - 6*x^2 + 2*x^3) / ((1 - x)*(1 - 3*x - 13*x^2 + 15*x^3 + 22*x^4 - 8*x^5)). - Colin Barker, Feb 23 2018
EXAMPLE
Some solutions for n=4:
..4..0..3..7....4..0..3..7....1..2..3..7....1..5..3..7....4..0..1..2
..5..1..2.11....5..1..2.11....0..9..5..6....0..4..2.11....8..6..7..3
.12..8..6.15....9.13..6.15....4.10.11.15....9.10..6.15...12..5.11.15
.13..9.10.14....8.12.10.14....8.12.13.14....8.12.13.14...13..9.10.14
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2012
STATUS
approved