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Search: id:A134293
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| A134293 |
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Number of ways to pair up {2..2n+1} so the sum of each pair is prime. |
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+0
2
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| 1, 1, 2, 6, 20, 60, 190, 764, 2337, 9812, 49538, 330058, 2133438, 11192143, 73469550, 462692414, 3692965270, 32635321384, 290171883863, 2572828730372
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OFFSET
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1,3
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COMMENT
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This sequence complements A000341, which is also related to A073364.
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FORMULA
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a(n)=permanent(m), where the n-by-n matrix m is defined m(i,j) = 1 or 0, depending on whether 2i+2j+1 is prime or composite, respectively.
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EXAMPLE
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a(3)=2 because for the set {2..7} there are two ways: {{2,3},{4,7},{5,6}} and {{2,5},{3,4},{6,7}}.
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CROSSREFS
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Sequence in context: A005628 A000620 A081251 this_sequence A136883 A057766 A132353
Adjacent sequences: A134290 A134291 A134292 this_sequence A134294 A134295 A134296
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Oct 17 2007
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