OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 29*a(n-1) - 175*a(n-2) + 147*a(n-3) for n>4.
Conjectures from Colin Barker, Oct 10 2018: (Start)
G.f.: x*(3 - 64*x + 234*x^2 - 98*x^3) / ((1 - x)*(1 - 7*x)*(1 - 21*x)).
a(n) = (2205 + 486*7^n + 125*21^n) / 3528 for n>1.
(End)
EXAMPLE
Some solutions for n=4:
..0..1..2..4....0..1..0..4....0..1..2..2....0..1..2..4....0..1..2..1
..2..1..0..1....0..1..2..1....1..0..2..2....2..2..4..3....1..2..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 06 2013
STATUS
approved