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A081383
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Least x=a(n) such that number of common prime-factors (ignoring multiplicity) of sigma[x]=A000203(x) and phi[x]=A000010(x) equals n.
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4
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OFFSET
| 1,1
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FORMULA
| a[n]=Min{x; A081396[x]=n}
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EXAMPLE
| n=209: sigma[209]=240=2.2.2.2.3.5,phi[209]=180=2.2.3.3.5, common-factor-set={2,3,5}, so a[209]=3.
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MATHEMATICA
| ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] t=Table[0, {10}]; Do[s=Length[Intersection[ba[EulerPhi[n]], ba[DivisorSigma[1, n]]]]; If[s<11&&t[[s]]==0, t[[s]]=n], {n, 1, 1000000}]; t
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CROSSREFS
| Cf. A000203, A000010, A081383.
Sequence in context: A108798 A132490 A058388 * A001320 A133028 A144985
Adjacent sequences: A081380 A081381 A081382 * A081384 A081385 A081386
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Mar 28 2003
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EXTENSIONS
| a(6)-a(8) from Donovan Johnson (donovan.johnson(AT)yahoo.com), May 24 2009
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