A221604 Number of n X 3 arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, without move-in move-out left turns.

2, 10, 54, 287, 1522, 8072, 42810, 227042, 1204112, 6385980, 33867896, 179617596, 952597728, 5052079816, 26793587384, 142099165304, 753619606464, 3996803992704, 21196956686208, 112417565028752, 596203932200160

Offset

1,1

Comments

Column 3 of A221609.

Links

R. H. Hardin, Table of n, a(n) for n = 1..65

Formula

Empirical: a(n) = 6*a(n-1) - 4*a(n-2) + 2*a(n-3) - 2*a(n-4).

Empirical g.f.: x*(2 - 2*x + 2*x^2 - x^3) / (1 - 6*x + 4*x^2 - 2*x^3 + 2*x^4). - Colin Barker, Aug 09 2018

Example

Some solutions for n=3:
..0..2..0....0..3..1....1..1..0....1..1..0....1..2..0....0..2..0....0..2..1
..2..2..0....1..0..0....0..3..1....1..3..0....0..2..0....1..2..1....0..2..2
..0..2..1....1..3..0....1..2..0....1..2..0....2..2..0....1..2..0....0..2..0

Crossrefs

Cf. A221609.

Sequence in context: A009322 A192697 A102536 * A163909 A272178 A152395

Adjacent sequences: A221601 A221602 A221603 * A221605 A221606 A221607

Keyword

nonn

Author

R. H. Hardin, Jan 20 2013

Status

approved