A221425 Number of n X 2 arrays of occupancy after each element moves to some horizontal or vertical neighbor, without consecutive moves in the same direction.

1, 9, 42, 217, 1116, 5722, 29383, 150821, 774219, 3974308, 20401353, 104726538, 537593996, 2759637891, 14166083083, 72718928341, 373288968420, 1916208848267, 9836498426064, 50493818235236, 259200537583569, 1330557304472777

Offset

1,2

Comments

Column 2 of A221429.

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 4*a(n-1) + 6*a(n-2) - 5*a(n-4) + a(n-5).

Empirical g.f.: x*(1 + 5*x - 5*x^3 + x^4) / (1 - 4*x - 6*x^2 + 5*x^4 - x^5). - Colin Barker, Aug 05 2018

Example

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

Crossrefs

Cf. A221429.

Sequence in context: A268622 A289364 A074443 * A007227 A224836 A195975

Adjacent sequences: A221422 A221423 A221424 * A221426 A221427 A221428

Keyword

nonn

Author

R. H. Hardin, Jan 15 2013

Status

approved