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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 January 18 21:06 EST 2021. Contains 340262 sequences. (Running on oeis4.)