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A203790
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Number of (n+1) X 3 0..3 arrays with every 2 X 2 subblock having equal diagonal elements or equal antidiagonal elements.
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1
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784, 10576, 142192, 1911952, 25708528, 345682576, 4648124656, 62499715984, 840385055728, 11300004020368, 151942362599152, 2043050737911184, 27471313768440304, 369385383417191056, 4966837867034125552
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 13*a(n-1) +6*a(n-2).
Empirical g.f.: 16*x*(49 + 24*x) / (1 - 13*x - 6*x^2). - Colin Barker, Jun 05 2018
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EXAMPLE
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Some solutions for n=4:
..0..2..3....0..1..0....1..3..2....1..0..0....3..2..2....3..1..3....2..1..1
..3..0..2....3..0..1....2..1..3....0..0..3....1..3..2....1..3..3....2..2..1
..2..3..0....1..3..0....2..2..1....1..0..0....1..1..3....3..1..3....0..2..2
..3..1..3....3..1..3....0..2..2....0..1..0....0..1..1....1..3..2....3..0..2
..1..3..3....0..3..0....2..2..1....1..3..1....0..0..1....3..0..3....2..3..0
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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