OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) +36*a(n-3) +9*a(n-4) -243*a(n-6) for n>7.
Empirical g.f.: x*(1 + 8*x + 8*x^2 + 12*x^3 - 72*x^4 + 36*x^5 + 144*x^6) / (1 - 2*x - 36*x^3 - 9*x^4 + 243*x^6). - Colin Barker, Jan 08 2019
EXAMPLE
Some solutions for n=4:
..1..5..3..7..8....1..5..6..4..8....1..5..3..4..8....1..2..3..4..8
..0.10..2.12..4....0.10..2..3.13....6.10..0.12..2....6.10..0..9.13
.11.15.13..6..9...11.15..7.14..9...11.15..7.17..9....5.12..7.14.18
.16.20.18.19.14...16.20.18.19.12...16.20.18.13.14...16.20.21.11.23
.21.22.23.24.17...21.22.23.24.17...21.22.23.24.19...15.22.17.24.19
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 18 2015
STATUS
approved