
OFFSET

1,1


COMMENTS

6.5*10^12 < a(3) <= 180577942272000000. We also have phi(sigma(n)) = 3*n for n = 144982963520227123200 and phi(sigma(n)) = 4*n for n = 16310583396025551360000 thus these may not be the smallest such n.  Giovanni Resta, Sep 13 2018


LINKS



EXAMPLE

phi(sigma(20575296))=phi(71238999)=41150592=2*20575296, so 20575296 is in the sequence.


MATHEMATICA

Do[If[EulerPhi[DivisorSigma[1, n]]==2n, Print[n]], {n, 350000000}]


CROSSREFS



KEYWORD

bref,more,nonn


AUTHOR



STATUS

approved

