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Search: id:A135239
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| A135239 |
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Numbers n such that sigma(phi(n))=2n. |
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+0
2
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OFFSET
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1,1
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COMMENT
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No other terms below 10^10.
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EXAMPLE
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sigma(phi(222850677))=sigma(118879488)=445701354=2*222850677, so 222850677 is in the sequence.
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MATHEMATICA
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Do[If[DivisorSigma[1, EulerPhi[n]]==2n, Print[n]], {n, 420000000}]
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CROSSREFS
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Cf. A135240.
Sequence in context: A156620 A133142 A068534 this_sequence A046043 A138480 A047627
Adjacent sequences: A135236 A135237 A135238 this_sequence A135240 A135241 A135242
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KEYWORD
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more,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 26 2007
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EXTENSIONS
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Search extended to 10^10 by Max Alekseyev (maxale(AT)gmail.com), Sep 25 2009
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