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A280896
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Number of n X 2 0..2 arrays with no element equal to more than one of its horizontal and antidiagonal neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards.
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1
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0, 1, 9, 124, 1464, 15768, 159920, 1554304, 14632704, 134378112, 1209699584, 10713166848, 93585811456, 808068888576, 6907767091200, 58538748477440, 492296387559424, 4112143740076032, 34141836642680832, 281936660687224832
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OFFSET
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1,3
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LINKS
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FORMULA
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Empirical: a(n) = 24*a(n-1) - 204*a(n-2) + 704*a(n-3) - 816*a(n-4) + 384*a(n-5) - 64*a(n-6) for n>8.
Empirical g.f.: x^2*(1 - 15*x + 112*x^2 - 380*x^3 + 408*x^4 - 192*x^5 + 32*x^6) / (1 - 8*x + 4*x^2)^3. - Colin Barker, Feb 14 2019
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EXAMPLE
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Some solutions for n=4:
..0..0. .0..1. .0..0. .0..1. .0..1. .0..0. .0..1. .0..1. .0..0. .0..0
..1..2. .2..2. .1..0. .1..1. .1..2. .1..0. .0..2. .1..1. .0..1. .1..1
..0..0. .0..0. .0..0. .2..1. .0..0. .1..1. .2..2. .1..2. .1..1. .1..0
..0..0. .0..0. .0..2. .1..1. .0..0. .1..1. .2..1. .0..1. .0..0. .0..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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