%I
%S 1,37044,1222452,193637687880
%N Numbers n such that geometric mean of phi(n), n and sigma(n) is an integer.
%C It is interesting that a(2) divides a(3).
%C There is no further term up to 6*10^8.
%C a(5) > 4*10^11.  _Giovanni Resta_, Jul 13 2013
%e (phi(1222452)*1222452*sigma(1222452))^(1/3)=1164240 is an integer, so 1222452 is a term of the sequence.
%t Do[If[IntegerQ[(n*DivisorSigma[1, n] EulerPhi[n])^(1/3)], Print[n]], {n, 600000000}]
%Y Cf. A011257.
%K more,nonn
%O 1,2
%A _Farideh Firoozbakht_, Dec 01 2005
%E a(4) from _Giovanni Resta_, Jul 13 2013
