OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) +4*a(n-2) +4*a(n-3).
Empirical g.f.: 4*x*(2 + 2*x + x^2) / (1 - 3*x - 4*x^2 - 4*x^3). - Colin Barker, Jan 07 2019
EXAMPLE
Some solutions for n=4:
..0..1..2..3....0..1..2..3....6..0..1..3....0..7..2..3....0..1..2..3
..4.11..5..6....4.11..6..7....4.11..2..7....4..1..5..6....4..5..6..7
..8..9.10..7...14..5..9.10...14..5..9.10....8.15..9.11....8..9.10.11
.12.19.14.15....8.19.13.15....8.19.13.15...18.13.10.14...12.19.13.14
.16.13.17.18...12.16.17.18...12.16.17.18...12.16.17.19...16.17.18.15
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 10 2015
STATUS
approved