A206384 Number of n X 3 0..6 arrays with no element equal to another within a city block distance of two, and new values 0..6 introduced in row major order.

1, 4, 55, 1368, 34442, 868994, 21916090, 552801398, 13943026782, 351682327314, 8870382111250, 223735362633678, 5643217340398022, 142337380859578634, 3590138049351706810, 90553101869397071558, 2283996915742293943662

Offset: 1

Author

R. H. Hardin, Feb 07 2012

Keywords

• nonn

Comments

Column 3 of A206389.

Examples

			Some solutions for n=4:
..0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2
..3..4..0....2..3..4....2..3..4....2..3..4....2..3..4....2..3..0....3..4..5
..1..2..5....4..5..6....4..5..6....4..5..0....1..0..5....1..4..5....5..2..1
..6..0..1....3..0..1....3..1..0....3..1..6....4..2..1....6..0..1....1..6..4
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..150

Crossrefs

Cf. A206389.

Formula

Empirical: a(n) = 21*a(n-1) + 131*a(n-2) - 637*a(n-3) + 486*a(n-4) for n>6.

Empirical g.f.: x*(1 - 17*x - 160*x^2 + 326*x^3 + 571*x^4 - 405*x^5) / ((1 - x)*(1 - 20*x - 151*x^2 + 486*x^3)). - Colin Barker, Jun 15 2018