A135239 Numbers m such that sigma(phi(m)) = 2*m.

1209, 27474741, 55385589, 222850677

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

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. A001229, A018784, A135240.

Sequence in context: A187862 A186864 A338963 * A046043 A358538 A359049

Adjacent sequences: A135236 A135237 A135238 * A135240 A135241 A135242

Keyword

more,nonn

Author

Farideh Firoozbakht, Dec 26 2007

Status

approved