A221420 Number of 2 X n arrays of occupancy after each element stays put or moves to some horizontal or antidiagonal neighbor, with every occupancy equal to zero or two.

0, 4, 10, 29, 84, 242, 696, 2000, 5744, 16492, 47344, 135900, 390080, 1119636, 3213616, 9223756, 26474016, 75985524, 218092816, 625967180, 1796642240, 5156696372, 14800673136, 42480669068, 121927372384, 349954089588

Offset

1,2

Comments

Row 2 of A221419.

Links

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

Formula

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

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

Example

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

Crossrefs

Cf. A221419.

Sequence in context: A026152 A025179 A116388 * A212262 A233347 A264158

Adjacent sequences: A221417 A221418 A221419 * A221421 A221422 A221423

Keyword

nonn

Author

R. H. Hardin, Jan 15 2013

Status

approved