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Search: id:A109810
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| A109810 |
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Number of permutations of the positive divisors of n, where every element is coprime to its adjacent elements. |
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+0
1
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| 1, 2, 2, 2, 2, 4, 2, 0, 2, 4, 2, 0, 2, 4, 4, 0, 2, 0, 2, 0, 4, 4, 2, 0, 2, 4, 0, 0, 2, 0, 2, 0, 4, 4, 4, 0, 2, 4, 4, 0, 2, 0, 2, 0, 0, 4, 2, 0, 2, 0, 4, 0, 2, 0, 4, 0, 4, 4, 2, 0, 2, 4, 0, 0, 4, 0, 2, 0, 4, 0, 2, 0, 2, 4, 0, 0, 4, 0, 2, 0, 0, 4, 2, 0, 4, 4, 4, 0, 2, 0, 4, 0, 4, 4, 4, 0, 2, 0, 0, 0, 2, 0, 2, 0, 0
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(1)=1, a(p) = 2, a(p^2) = 2, a(p*q) = 4 (where p and q are distinct primes), all other terms are 0.
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EXAMPLE
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The divisors of 6 are 1, 2, 3, and 6. Of the permutations of these integers,
only (6,1,2,3), (6,1,3,2), (2,3,1,6) and (3,2,1,6) are such that every pair of adjacent elements is coprime.
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CROSSREFS
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Adjacent sequences: A109807 A109808 A109809 this_sequence A109811 A109812 A109813
Sequence in context: A062816 A122857 A132003 this_sequence A122066 A053238 A058263
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KEYWORD
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nonn,new
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Aug 16 2005
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EXTENSIONS
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Terms 17 to 59 from Diana Mecum (diana.mecum(AT)gmail.com), Jul 18 2008
More terms from David Wasserman (dwasserm(AT)earthlink.net), Oct 01 2008
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