OFFSET
1,2
COMMENTS
Column 4 of A224333.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
a(n) = n*(2*5^(n-1)-1).
a(n) = 12*a(n-1) - 46*a(n-2) + 60*a(n-3) - 25*a(n-4).
G.f.: x*(1 + 6*x - 23*x^2) / ((1 - x)^2*(1 - 5*x)^2). - Colin Barker, Aug 29 2018
EXAMPLE
Some solutions for n=3:
..0..0..0....1..0..0....0..4..2....1..0..0....1..0..0....1..0..0....1..2..0
..3..1..0....0..1..2....0..1..0....1..0..3....0..1..3....0..0..0....0..0..0
..3..0..1....0..0..0....0..0..1....0..0..1....0..0..0....0..0..1....0..0..1
PROG
(PARI) Vec(x*(1 + 6*x - 23*x^2) / ((1 - x)^2*(1 - 5*x)^2) + O(x^40)) \\ Colin Barker, Aug 29 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
R. H. Hardin, formula via M. F. Hasler William J. Keith and Rob Pratt in the Sequence Fans Mailing List, Apr 03 2013
STATUS
approved