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Search: id:A140748
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| A140748 |
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a(n) = the number of divisors of n that are each not coprime to the next larger divisor of n. |
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+0
2
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| 0, 0, 0, 1, 0, 1, 0, 2, 1, 1, 0, 2, 0, 1, 1, 3, 0, 3, 0, 3, 1, 1, 0, 4, 1, 1, 2, 3, 0, 3, 0, 4, 1, 1, 1, 5, 0, 1, 1, 4, 0, 4, 0, 3, 2, 1, 0, 6, 1, 3, 1, 3, 0, 5, 1, 4, 1, 1, 0, 6, 0, 1, 2, 5, 1, 4, 0, 3, 1, 3, 0, 7, 0, 1, 3, 3, 1, 4, 0, 6, 3, 1, 0, 6, 1, 1, 1, 5, 0, 6, 1, 3, 1, 1, 1, 8, 0, 3, 3, 6, 0, 4, 0, 5, 3
(list; graph; listen)
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OFFSET
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1,8
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COMMENT
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A140747(n) + A140748(n) = d(n) -1, where d(n) is the number of divisors of n.
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LINKS
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Leroy Quet, Home Page (listed in lieu of email address)
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EXAMPLE
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The divisors of 20 are 1,2,4,5,10,20. 1 is coprime to 2. 2 is not coprime to 4. 4 is coprime to 5. 5 is not coprime to 10. And 10 is not coprime to 20. So there are 3 divisors, 2, 5 and 10, that are each not coprime to the next higher divisor. So a(20) = 3.
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CROSSREFS
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Cf. A140747, A136164, A136165, A136166, A136167.
Sequence in context: A143439 A105469 A136167 this_sequence A070821 A165890 A051632
Adjacent sequences: A140745 A140746 A140747 this_sequence A140749 A140750 A140751
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet, May 26 2008
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EXTENSIONS
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Extended by Max Alekseyev (maxale(AT)gmail.com), Mar 12 2009
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