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Search: id:A163436
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| A163436 |
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Number of different fixed (possibly) disconnected n-ominoes bounded tightly by an n*n square |
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+0
2
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| 1, 2, 22, 425, 11550, 403252, 17164532, 860938920, 49684113582, 3240906864140, 235707022877304, 18906047682170948, 1657638292334575486, 157698852357527675040, 16177213677228994535040
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OFFSET
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1,2
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FORMULA
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a(n)=binomial(n^2,n)-4*binomial((n-1)*n,n)+4*binomial((n-1)^2,n)+2*binomial((n-2)*n,n)-4*binomial((n-2)*(n-1),n)+binomial((n-2)^2,n), n>1
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EXAMPLE
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a(2)=2: the two rotations of the strictly disconnected domino consisting of two squares connected at a vertex
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CROSSREFS
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Cf. A162676, A163437
Sequence in context: A138463 A007842 A013519 this_sequence A084949 A137076 A090730
Adjacent sequences: A163433 A163434 A163435 this_sequence A163437 A163438 A163439
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KEYWORD
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nonn
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AUTHOR
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David Bevan (dbevan(AT)emtex.com), Jul 28 2009
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