OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) - 13*a(n-2) - 12*a(n-3).
Conjectures from Colin Barker, Jan 27 2019: (Start)
G.f.: 5*x*(1 - 3*x - 2*x^2) / ((1 - 4*x)*(1 - 4*x - 3*x^2)).
a(n) = (-5/42)*(7*4^n + (2-sqrt(7))^n*(-7+3*sqrt(7)) - (2+sqrt(7))^n*(7+3*sqrt(7))).
(End)
EXAMPLE
Some solutions for n=7:
..3. .0. .4. .1. .2. .2. .2. .3. .2. .3. .3. .0. .0. .2. .2. .3
..1. .3. .2. .3. .4. .0. .3. .0. .2. .1. .4. .0. .2. .2. .0. .3
..2. .0. .3. .0. .0. .1. .1. .2. .2. .0. .1. .4. .2. .2. .3. .4
..2. .4. .2. .2. .3. .1. .1. .1. .2. .0. .0. .1. .2. .3. .0. .2
..2. .3. .3. .1. .0. .0. .1. .3. .4. .0. .0. .0. .4. .4. .3. .3
..2. .3. .2. .4. .2. .1. .3. .2. .2. .2. .2. .2. .3. .0. .2. .2
..1. .3. .3. .0. .3. .2. .4. .4. .1. .3. .4. .4. .1. .4. .0. .4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 03 2016
STATUS
approved