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A135239 Numbers m such that sigma(phi(m)) = 2*m. 1
1209, 27474741, 55385589, 222850677 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
From Max Alekseyev, Oct 12 2023: (Start)
No other terms below 3*10^11.
If a term m is odd, then phi(m) belongs to A001229; otherwise phi(m) belongs to A135240. (End)
LINKS
EXAMPLE
sigma(phi(222850677)) = sigma(118879488) = 445701354 = 2*222850677, so 222850677 is in the sequence.
MATHEMATICA
Do[If[DivisorSigma[1, EulerPhi[n]]==2n, Print[n]], {n, 420000000}]
CROSSREFS
Sequence in context: A187862 A186864 A338963 * A046043 A358538 A359049
KEYWORD
more,nonn
AUTHOR
Farideh Firoozbakht, Dec 26 2007
STATUS
approved

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Last modified June 25 02:21 EDT 2024. Contains 373691 sequences. (Running on oeis4.)