A068579 - OEIS

%I #16 Jun 12 2022 02:58:52

%S 1,11,13,19,33,34,35,39,46,57,58,62,74,86,88,102,104,105,110,130,135,

%T 138,152,154,174,182,186,190,222,258,264,280,312,330,342,390,456,462,

%U 546,570,594,756,840,1080

%N Let phi_m(x) = phi(phi(...(phi(x))...)) m times; sequence gives values of k such that phi_3(k) = tau(k).

%C Numbers k such that A049099(k) = A000005(k).

%t Select[Range[1080], Nest[EulerPhi, #, 3] === DivisorSigma[0, #] &] (* _Amiram Eldar_, Jun 12 2022 *)

%o (PARI) is(k) = numdiv(k) == eulerphi(eulerphi(eulerphi(k))); \\ _Jinyuan Wang_, Apr 05 2020

%Y Cf. A000005, A000010, A049099, A068580, A068581, A068582.

%K nonn,easy,fini,full

%O 1,2

%A _Benoit Cloitre_, Mar 26 2002