This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A068579 #16 Jun 12 2022 02:58:52 %S A068579 1,11,13,19,33,34,35,39,46,57,58,62,74,86,88,102,104,105,110,130,135, %T A068579 138,152,154,174,182,186,190,222,258,264,280,312,330,342,390,456,462, %U A068579 546,570,594,756,840,1080 %N A068579 Let phi_m(x) = phi(phi(...(phi(x))...)) m times; sequence gives values of k such that phi_3(k) = tau(k). %C A068579 Numbers k such that A049099(k) = A000005(k). %t A068579 Select[Range[1080], Nest[EulerPhi, #, 3] === DivisorSigma[0, #] &] (* _Amiram Eldar_, Jun 12 2022 *) %o A068579 (PARI) is(k) = numdiv(k) == eulerphi(eulerphi(eulerphi(k))); \\ _Jinyuan Wang_, Apr 05 2020 %Y A068579 Cf. A000005, A000010, A049099, A068580, A068581, A068582. %K A068579 nonn,easy,fini,full %O A068579 1,2 %A A068579 _Benoit Cloitre_, Mar 26 2002