OFFSET
1,1
COMMENTS
Column 2 of A269109.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 14*a(n-1) - 49*a(n-2) for n>3.
Conjectures from Colin Barker, Mar 21 2018: (Start)
G.f.: 4*x*(4 - 11*x + x^2) / (1 - 7*x)^2.
a(n) = 60*7^(n-3)*(8*n+5) for n>1.
(End)
EXAMPLE
Some solutions for n=4:
..2..2. .2..0. .2..2. .1..0. .3..3. .3..1. .1..3. .3..1. .1..3. .1..0
..0..2. .2..0. .2..3. .3..1. .3..1. .3..3. .3..1. .3..1. .1..3. .3..1
..1..0. .0..2. .2..3. .1..1. .2..2. .2..2. .3..3. .1..3. .0..1. .0..1
..1..0. .1..0. .1..1. .1..1. .3..3. .3..0. .1..3. .3..1. .0..0. .2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 19 2016
STATUS
approved