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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. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 24 00:38 EST 2020. Contains 332195 sequences. (Running on oeis4.)