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 A066670 #23 Aug 15 2025 23:18:11
%S A066670 3,3,5,3,3,3,3,5,11,5,3,3,7,5,3,3,3,5,3,5,3,11,23,5,3,13,5,3,7,29,3,5,
%T A066670 11,3,3,5,3,5,41,3,7,5,11,3,11,23,3,5,3,3,13,53,5,3,7,11,7,29,3,5,3,5,
%U A066670 17,11,3,23,3,7,37,5,3,3,13,5,5,41,83,3,43,7,5,29,11,89,3,11,5,23,3,3
%N A066670 Primes arising in A066669: the only odd prime divisor of phi(A066669(n)).
%H A066670 Michael De Vlieger, <a href="/A066670/b066670.txt">Table of n, a(n) for n = 1..10000</a>
%F A066670 From _Amiram Eldar_, Jul 18 2024: (Start)
%F A066670 a(n) = A053575(A066669(n)).
%F A066670 a(n) = A000265(A000010(A066669(n))) = A006530(A000010(A066669(n))). (End)
%e A066670 A066669(9) = 23, phi(23) = 2*11, so a(9)=11.
%t A066670 Select[Array[#/2^IntegerExponent[#, 2] &@ EulerPhi@ # &, 200], PrimeQ] (* _Michael De Vlieger_, Dec 08 2018 *)
%o A066670 (PARI) lista(nn) = {for (n=1, nn, en=eulerphi(n); if (isprime(p=en>>valuation(en, 2)), print1(p, ", ")); ); } \\ _Michel Marcus_, Dec 08 2018
%Y A066670 Cf. A000010, A000265, A053575, A006530, A065966, A066669, A066671, A066672, A066673.
%K A066670 nonn
%O A066670 1,1
%A A066670 _Labos Elemer_, Dec 18 2001