A221756 Number of 2 X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, without move-in move-out straight through or left turns.

0, 2, 1, 9, 17, 64, 171, 536, 1558, 4689, 13889, 41437, 123228, 366983, 1092232, 3251610, 9679073, 28813033, 85770153, 255320984, 760038643, 2262482568, 6734954798, 20048604913, 59680661697, 177657315701, 528850071604

Offset

1,2

Comments

Row 2 of A221755.

Links

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

Formula

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

Empirical g.f.: x^2*(2 - x - 4*x^2) / (1 - x - 6*x^2 - x^3 + 4*x^4). - Colin Barker, Aug 10 2018

Example

Single solution for n=3:
..0..2..1
..1..2..0

Crossrefs

Cf. A221755.

Sequence in context: A214884 A083162 A178075 * A094633 A261060 A144244

Adjacent sequences: A221753 A221754 A221755 * A221757 A221758 A221759

Keyword

nonn

Author

R. H. Hardin, Jan 24 2013

Status

approved