%I #10 May 13 2013 01:49:40
%S 1,2,4,6,18
%N Numbers n such that phi(n) divides rad(n).
%C Terms are all of the form n = 2^a * 3^b with a <= 2 (else 4 | rad(n)) and b <= 2 (else 9 | rad(n)), hence the sequence is finite. [_Charles R Greathouse IV_, Jun 29 2011]
%t Rad[n_] := Times @@ Transpose[FactorInteger[n]][[1]]; Select[Range[10^6], Mod[Rad[#], EulerPhi[#]] == 0 &]
%o (PARI) rad(n)=n=factor(n)[,1];prod(i=1,#n,n[i])
%o for(n=1,2^2*3^2,if(rad(n)%eulerphi(n)==0,print1(n", "))) \\ _Charles R Greathouse IV_, Jun 29 2011
%Y Cf. A000010, A007947.
%K nonn,fini,full
%O 1,2
%A _José María Grau Ribas_, Jun 28 2011