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A067740
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Smallest number k such that sigma(k)/sigma(phi(k)) = n.
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1
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OFFSET
| 1,2
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COMMENTS
| The quotient sigma(k)/sigma(phi(k)) is integral for the numbers in A190503. Does a(n) exist for all n?
10^11 < a(8) <= 11224976029787520. - Donovan Johnson, Jun 07 2011
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FORMULA
| a(n)=Min{x; A000203(x)/A000203[A000010(x)]=n}
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EXAMPLE
| n=6, a(6)=2915640, sigma(2915640)=11793600, phi(2915640)=608256, sigma(608256)=1965600 and 11793600=6*1965600.
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MATHEMATICA
| g[x_] := DivisorSigma[1, x] / DivisorSigma[1, EulerPhi[x]]; m=10; up=200000; a = Table[0, {m}]; Do[ b = g[n]; If[b <= m && IntegerQ[b] && a[[b]] == 0, a[[b]] = n], {n, 1, up} ]; a
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CROSSREFS
| Cf. A000203, A000010, A067385, A190503.
Sequence in context: A040194 A107834 A070701 * A037923 A040195 A040189
Adjacent sequences: A067737 A067738 A067739 * A067741 A067742 A067743
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KEYWORD
| more,nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jan 29 2002
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EXTENSIONS
| a(7) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jun 07 2011
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