OFFSET
1,1
COMMENTS
Column 4 of A221623.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 24*a(n-1) - 166*a(n-2) + 264*a(n-3) - 121*a(n-4).
Conjectures from Colin Barker, Aug 09 2018: (Start)
G.f.: x*(12 - 11*x)*(2 - 12*x + 11*x^2) / ((1 - x)^2*(1 - 11*x)^2).
a(n) = (4*(4+11^(2+n)) + 5*(1+11^(2+n))*n) / 500.
(End)
EXAMPLE
Some solutions for n=3:
..2..4..1..3....2..1..3..4....3..4..1..2....3..4..2..1....2..1..4..3
..3..2..1..4....2..4..1..3....1..2..4..3....4..1..3..2....3..2..4..1
..4..3..1..2....3..1..2..4....2..4..3..1....4..3..2..1....1..4..3..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 21 2013
STATUS
approved