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 A230904 Number of n X 2 0..3 arrays x(i,j) with each element horizontally, vertically or antidiagonally next to at least one element with value (x(i,j)+1) mod 4, no adjacent elements equal, and upper left element zero. 1
 0, 2, 8, 26, 84, 272, 882, 2862, 9290, 30160, 97922, 317940, 1032328, 3351922, 10883582, 35338706, 114743960, 372571146, 1209730676, 3927970464, 12754039410, 41412104942, 134464258714, 436602703328, 1417640069298, 4603048385236 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 5*a(n-1) -6*a(n-2) +a(n-3) for n>4. Empirical g.f.: 2*x^2*(1 - x - x^2) / (1 - 5*x + 6*x^2 - x^3). - Colin Barker, Sep 22 2018 EXAMPLE Some solutions for n=4: ..0..1....0..1....0..3....0..1....0..1....0..1....0..1....0..3....0..3....0..1 ..2..0....3..2....1..2....2..3....2..0....2..3....2..3....1..0....1..2....3..2 ..3..2....0..3....0..3....1..0....3..1....0..1....0..2....2..3....0..1....0..1 ..0..1....1..2....2..1....2..3....2..0....3..2....1..0....1..0....3..2....3..2 CROSSREFS Column 2 of A230910. Sequence in context: A002930 A060410 A128634 * A289595 A298189 A053956 Adjacent sequences:  A230901 A230902 A230903 * A230905 A230906 A230907 KEYWORD nonn AUTHOR R. H. Hardin, Nov 01 2013 STATUS approved

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Last modified February 16 20:45 EST 2019. Contains 320189 sequences. (Running on oeis4.)