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A030230
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Numbers n such that number of distinct primes dividing n is odd.
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4
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2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 23, 25, 27, 29, 30, 31, 32, 37, 41, 42, 43, 47, 49, 53, 59, 60, 61, 64, 66, 67, 70, 71, 73, 78, 79, 81, 83, 84, 89, 90, 97, 101, 102, 103, 105, 107, 109, 110, 113, 114, 120, 121, 125, 126, 127, 128, 130, 131, 132, 137, 138, 139, 140, 149
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| GCD[A008472(a[n]), A007947(a[n])]>1; see A014963. - Labos E. (labos(AT)ana.sote.hu), Mar 26 2003
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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FORMULA
| n such that sum(d|n, mu(d)*tau(d))=(-1)^omega(n)=-1 where mu(d)=A008683(d), tau(d)=A000005(d) and omega(d)=A001221(d). - Benoit Cloitre, Dec 08 2002
n such that sum(d|n, mu(d)*tau(d))=(-1)^omega(n)=-1 where mu(d)=A008683(d), tau(d)=A000005(d) and omega(d)=A001221(d). n such that A023900(n)<0 - Benoit Cloitre, Dec 08 2002
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MATHEMATICA
| (* Prior to version 7.0 *) littleOmega[n_] := Length[FactorInteger[n]]; Select[ Range[2, 149], (-1)^littleOmega[#] == -1 &] (* From Jean-François Alcover, Nov 30 2011, after Benoit Cloitre *)
(* Version 7.0+ *) Select[Range[2, 149], (-1)^PrimeNu[#] == -1 &]
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PROG
| (Haskell)
a030230 n = a030230_list !! (n-1)
a030230_list = filter (odd . a001221) [1..]
-- Reinhard Zumkeller, Aug 14 2011
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CROSSREFS
| Cf. A030231.
Sequence in context: A133811 A119314 A014567 * A089352 A086486 A071139
Adjacent sequences: A030227 A030228 A030229 * A030231 A030232 A030233
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KEYWORD
| nonn,easy,nice
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AUTHOR
| David W. Wilson (davidwwilson(AT)comcast.net)
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