OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) - 5*a(n-2) + 36*a(n-3) - 72*a(n-4) - 243*a(n-6) for n>7.
Empirical g.f.: x*(1 + 2*x - 3*x^2 + 4*x^3 + 72*x^4 + 144*x^5 + 171*x^6) / ((1 - x - 9*x^3)*(1 - 5*x - 27*x^3)). - Colin Barker, Jan 07 2019
EXAMPLE
Some solutions for n=4:
..1..5..6..7..8....1..2..6..7..8....1..5..6..7..8....1..5..3..7..8
..0..2..3.12..4....0.10..3..4.13....0..2..3.12..4....0.10..2..4.13
.11.15.16.14..9....5.15.16.14..9...11.15.16.14..9....6.12.16..9.18
.10.20.13.22.23...11.20.12.22.23...10.20.18.13.23...11.20.21.22.14
.21.17.18.24.19...21.17.18.24.19...21.22.17.24.19...15.17.23.24.19
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 11 2015
STATUS
approved