OFFSET
1,1
COMMENTS
Column 4 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-2) +a(n-3) +4*a(n-4) +a(n-6) +a(n-7).
Empirical g.f.: x*(65 + 47*x^2 + 102*x^3 + 10*x^4 + 30*x^5 + 25*x^6) / (1 - 3*x + x^2 - x^3 - 4*x^4 - x^6 - x^7). - Colin Barker, Oct 16 2017
EXAMPLE
Some solutions for n=3
..0....1....4....1....1....0....4....0....2....0....2....0....3....4....4....4
..0....4....2....2....4....1....4....0....3....0....2....1....4....1....0....4
..2....4....2....2....4....1....4....1....3....1....0....4....4....0....0....1
..2....4....3....1....2....3....2....1....2....3....0....4....3....0....2....1
..3....3....3....1....2....4....1....1....1....4....1....2....1....3....3....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, 5}]; a[n_] := Sum[a[n, x, y], {x, 5}, {y, 5}]; Array[a, 25] (* Giovanni Resta, Mar 05 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 23 2011
STATUS
approved