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Search: id:A112728
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| A112728 |
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Numbers n such that geometric mean of phi(n), n and sigma(n) is an integer. |
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+0
1
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OFFSET
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1,2
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COMMENT
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It is interesting that a(2) divides a(3).
There is no further term up to 6*10^8.
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EXAMPLE
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(phi(1222452)*1222452*sigma(1222452))^(1/3)=1164240 is an integer, so 1222452 is a term of the sequence.
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MATHEMATICA
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Do[If[IntegerQ[(n*DivisorSigma[1, n] EulerPhi[n])^(1/3)], Print[n]], {n, 600000000}]
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CROSSREFS
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Cf. A011257.
Sequence in context: A061739 A051393 A057881 this_sequence A022245 A092682 A048526
Adjacent sequences: A112725 A112726 A112727 this_sequence A112729 A112730 A112731
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KEYWORD
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more,nonn,bref
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AUTHOR
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Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Dec 01 2005
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