OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 10*a(n-1) - 35*a(n-2) + 50*a(n-3) - 24*a(n-4); a(n) = (52650*4^n - 80640*3^n + 35820*2^n - 2688)/12.
Empirical g.f.: 4*x*(784 - 2481*x + 4604*x^2 - 2571*x^3) / ((1 - x)*(1 - 2*x)*(1 - 3*x)*(1 - 4*x)). - Colin Barker, Nov 21 2018
EXAMPLE
Some solutions for n=3:
..3..3..1..1..1....3..3..2..2..3....2..2..1..1..1....2..1..1..1..1
..0..0..0..0..1....0..0..0..0..1....0..0..0..0..0....1..1..1..1..1
..0..0..0..0..1....0..0..1..2..3....0..0..2..2..2....1..1..1..1..1
..0..0..0..1..2....0..0..1..2..3....0..1..3..3..3....0..0..1..2..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 28 2014
STATUS
approved