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 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
 1, 9, 42, 217, 1116, 5722, 29383, 150821, 774219, 3974308, 20401353, 104726538, 537593996, 2759637891, 14166083083, 72718928341, 373288968420, 1916208848267, 9836498426064, 50493818235236, 259200537583569, 1330557304472777 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified May 26 15:29 EDT 2019. Contains 323597 sequences. (Running on oeis4.)