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Search: id:A128830
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| A128830 |
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a(n) = the number of positive divisors of n which are coprime to d(n), where d(n) = the number of positive divisors of n. |
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2
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| 1, 1, 2, 3, 2, 2, 2, 1, 1, 2, 2, 1, 2, 2, 4, 5, 2, 1, 2, 2, 4, 2, 2, 2, 3, 2, 4, 2, 2, 4, 2, 1, 4, 2, 4, 3, 2, 2, 4, 2, 2, 4, 2, 2, 2, 2, 2, 2, 3, 3, 4, 2, 2, 4, 4, 2, 4, 2, 2, 2, 2, 2, 2, 7, 4, 4, 2, 2, 4, 4, 2, 1, 2, 2, 3, 2, 4, 4, 2, 1, 5, 2, 2, 2, 4, 2, 4, 2, 2, 2, 4, 2, 4, 2, 4, 1, 2, 3, 2, 9, 2, 4, 2, 2, 8
(list; graph; listen)
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OFFSET
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1,3
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EXAMPLE
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The 6 positive divisors of 20 are 1,2,4,5,10,20. Of these, only 1 and 5 are coprime to d(20) = 6. So a(20) = 2.
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MAPLE
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with(numtheory): a:=proc(n) local div, ct, i: div:=divisors(n): ct:=0: for i from 1 to tau(n) do if igcd(div[i], tau(n))=1 then ct:=ct+1 else ct:=ct: fi od: ct; end: seq(a(n), n=1..140); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 14 2007
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CROSSREFS
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Sequence in context: A114729 A049342 A112966 this_sequence A090387 A030329 A120881
Adjacent sequences: A128827 A128828 A128829 this_sequence A128831 A128832 A128833
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Apr 13 2007
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 14 2007
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