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Search: id:A138010
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| A138010 |
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a(n) = number of positive divisors of n that each divide d(n). (d(n) = number of positive divisors of n.) a(n) also equals d(GCD(n,d(n))). |
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+0
3
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| 1, 2, 1, 1, 1, 2, 1, 3, 2, 2, 1, 4, 1, 2, 1, 1, 1, 4, 1, 2, 1, 2, 1, 4, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 4, 1, 2, 1, 6, 1, 2, 2, 1, 1, 2, 1, 2, 1, 2, 1, 6, 1, 2, 2, 2, 1, 2, 1, 4, 1, 2, 1, 6, 1, 2, 1, 4, 1, 4, 1, 2, 1, 2, 1, 6, 1, 2, 2, 1
(list; graph; listen)
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OFFSET
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1,2
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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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12 has 6 divisors (1,2,3,4,6,12). Those divisors of 12 that divide 6 are 1,2,3,6. Since there are 4 of these, then a(12) = 4.
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MAPLE
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with(numtheory): a:=proc(n) local div, c, j: div:=divisors(n): c:=0: for j to tau(n) do if `mod`(tau(n), div[j])=0 then c:=c+1 else end if end do: c end proc: seq(a(n), n=1..90); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 02 2008
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MATHEMATICA
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Table[Length[Select[Divisors[n], Mod[Length[Divisors[n]], # ] == 0 &]], {n, 1, 100}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Feb 29 2008
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CROSSREFS
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Cf. A138011, A138012.
Sequence in context: A085091 A052128 A114536 this_sequence A167204 A104306 A074389
Adjacent sequences: A138007 A138008 A138009 this_sequence A138011 A138012 A138013
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet, Feb 27 2008
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 29 2008
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