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A135239 Numbers n such that sigma(phi(n))=2n. 1

%I

%S 1209,27474741,55385589,222850677

%N Numbers n such that sigma(phi(n))=2n.

%C No other terms below 10^10.

%e sigma(phi(222850677))=sigma(118879488)=445701354=2*222850677, so 222850677 is in the sequence.

%t Do[If[DivisorSigma[1,EulerPhi[n]]==2n,Print[n]],{n,420000000}]

%Y Cf. A135240.

%K more,nonn

%O 1,1

%A _Farideh Firoozbakht_, Dec 26 2007

%E Search extended to 10^10 by _Max Alekseyev_, Sep 25 2009

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Last modified November 16 20:08 EST 2019. Contains 329204 sequences. (Running on oeis4.)