OFFSET
1,1
COMMENTS
This is the subsequence of nonsquarefree elements of A137815. See there for more comments and references.
There are only 32 such numbers below 10^6, 145 below 10^7 and 785 below 10^8.
LINKS
M. F. Hasler, Table of n, a(n) for n=1,...,785.
MATHEMATICA
Reap[For[n=1, n<10^6, n++, If[!SquareFreeQ[n] && EulerPhi[n] == 2*EulerPhi[ DivisorSigma[1, n]], Print[n]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, Dec 12 2016 *)
PROG
(PARI) for( n=1, 10^6, !issquarefree(n) && eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved