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A135239 Numbers n such that sigma(phi(n))=2n. 1
1209, 27474741, 55385589, 222850677 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No other terms below 10^10.

LINKS

Table of n, a(n) for n=1..4.

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

Cf. A135240.

Sequence in context: A279983 A187862 A186864 * A046043 A138480 A047627

Adjacent sequences:  A135236 A135237 A135238 * A135240 A135241 A135242

KEYWORD

more,nonn

AUTHOR

Farideh Firoozbakht, Dec 26 2007

EXTENSIONS

Search extended to 10^10 by Max Alekseyev, Sep 25 2009

STATUS

approved

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Last modified October 21 12:12 EDT 2019. Contains 328299 sequences. (Running on oeis4.)