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 A221304 Number of n X 2 arrays of occupancy after each element moves to some horizontal, vertical or antidiagonal neighbor, with every occupancy equal to zero or two. 1
 0, 5, 10, 31, 90, 259, 746, 2150, 6192, 17831, 51346, 147850, 425724, 1225834, 3529664, 10163285, 29264046, 84262511, 242624302, 698608939, 2011564422, 5792069134, 16677598712, 48021232079, 138271627638, 398137284986 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Column 2 of A221308. 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) + a(n-6). Empirical g.f.: x^2*(5 - 10*x + 6*x^2 - 4*x^3 + 2*x^4) / ((1 - 3*x + x^3)*(1 - x - x^3)). - Colin Barker, Aug 05 2018 EXAMPLE All solutions for n=3: ..0..0....0..2....2..2....0..2....0..2....2..0....0..2....2..0....0..0....0..0 ..2..0....2..2....0..2....0..2....0..2....2..0....2..0....2..2....2..2....2..2 ..2..2....0..0....0..0....2..0....0..2....2..0....2..0....0..0....2..0....0..2 CROSSREFS Cf. A221308. Sequence in context: A020995 A174467 A005201 * A094234 A052538 A240413 Adjacent sequences: A221301 A221302 A221303 * A221305 A221306 A221307 KEYWORD nonn AUTHOR R. H. Hardin, Jan 09 2013 STATUS approved

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Last modified April 1 22:19 EDT 2023. Contains 361716 sequences. (Running on oeis4.)