

A137600


Numbers n such that sigma(sigma(n))phi(phi(n)) = 3n.


4




OFFSET

1,1


COMMENTS

If 2^p1 is a Mersenne prime then n=9*2^(p1) is in the sequence (the proof is easy). 18, 36, 144, 576, 36864, 589824 & 2359296 are such terms. 32 is in the sequence but it is not of this form.


LINKS



MATHEMATICA

Do[If[DivisorSigma[1, DivisorSigma[1, n]]EulerPhi[EulerPhi[n]]==3n, Print[n]], {n, 25000000}]


CROSSREFS



KEYWORD

more,nonn


AUTHOR



EXTENSIONS



STATUS

approved



