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A198900
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Number of n X 2 0..4 arrays with values 0..4 introduced in row major order and no element equal to any horizontal or vertical neighbor.
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5
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1, 4, 33, 380, 4801, 62004, 804833, 10459180, 135958401, 1767426404, 22976444833, 298693487580, 3883014452801, 50479185229204, 656229400008033, 8530982176189580, 110902768218720001, 1441735986628126404
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 17*a(n-1) -55*a(n-2) +39*a(n-3).
G.f.: x*(1 - 13*x + 20*x^2) / ((1 - x)*(1 - 3*x)*(1 - 13*x)).
a(n) = (26 + 13*3^n + 13^n) / 78.
(End)
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EXAMPLE
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Some solutions with values 0 to 4 for n=4:
..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..2..3....2..3....2..0....1..2....1..0....2..3....2..3....2..3....1..2....2..3
..4..2....1..4....3..2....3..1....2..3....1..4....3..1....4..2....2..3....4..0
..2..4....3..2....4..3....2..4....4..2....4..3....4..2....2..0....4..0....0..3
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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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