OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) - 12*a(n-2) - 16*a(n-3).
Empirical g.f.: 5*x*(1 - 3*x - 3*x^2) / ((1 - 4*x)*(1 - 4*x - 4*x^2)). - Colin Barker, Jan 29 2019
EXAMPLE
Some solutions for n=7:
..2. .2. .4. .4. .3. .2. .1. .4. .4. .1. .0. .3. .4. .4. .0. .3
..4. .0. .2. .1. .1. .2. .2. .0. .1. .2. .4. .1. .4. .2. .3. .3
..1. .1. .2. .3. .0. .0. .1. .2. .2. .0. .3. .0. .4. .4. .1. .1
..3. .0. .2. .3. .3. .2. .3. .1. .1. .4. .4. .3. .4. .3. .1. .2
..2. .1. .1. .3. .0. .2. .2. .4. .3. .3. .1. .4. .2. .2. .0. .4
..3. .4. .4. .2. .2. .4. .0. .0. .2. .1. .0. .4. .4. .1. .4. .0
..0. .1. .1. .2. .2. .0. .3. .3. .2. .0. .2. .1. .4. .3. .0. .4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 04 2016
STATUS
approved