OFFSET
1,1
COMMENTS
Column 5 of A200871.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + a(n-3) + 7*a(n-4) + 3*a(n-5) + 2*a(n-6) + 3*a(n-7) + a(n-8).
Empirical g.f.: 2*x*(53 + 19*x + 50*x^2 + 138*x^3 + 67*x^4 + 48*x^5 + 57*x^6 + 18*x^7) / (1 - 3*x - x^3 - 7*x^4 - 3*x^5 - 2*x^6 - 3*x^7 - x^8). - Colin Barker, Oct 16 2017
EXAMPLE
Some solutions for n=3
..0....3....5....1....1....4....0....5....1....3....5....3....5....2....0....3
..1....0....5....1....0....0....2....3....1....5....0....0....2....0....0....5
..4....0....5....1....0....0....5....2....3....5....0....0....1....0....2....5
..4....1....5....0....0....2....5....2....3....2....3....2....1....5....3....4
..4....1....4....0....2....5....5....5....4....2....4....5....3....5....4....0
MATHEMATICA
a[0, x_, y_] := 1; a[n_, x_, y_] := a[n, x, y] = Sum[If[z <= x <= y || y <= x <= z, a[n - 1, z, x], 0], {z, 6}]; a[n_] := Sum[a[n, x, y], {x, 6}, {y, 6}]; Array[a, 25] (* Giovanni Resta, Mar 06 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 23 2011
STATUS
approved