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 A066671 #24 Aug 16 2025 03:17:25
%S A066671 2,2,2,4,2,2,4,2,2,4,4,4,4,4,8,4,8,8,4,4,8,2,2,4,8,4,8,8,4,2,16,4,4,8,
%T A066671 8,8,8,8,2,8,8,8,8,8,4,2,32,8,16,16,4,2,8,16,16,8,8,2,32,16,16,8,8,4,
%U A066671 16,4,16,16,4,8,32,16,8,16,16,2,2,16,4,8,16,4,8,2,16,8,32,4,64,32,32
%N A066671 a(n) is the largest power of 2 that divides phi(A066669(n)).
%H A066671 Michael De Vlieger, <a href="/A066671/b066671.txt">Table of n, a(n) for n = 1..10000</a>
%F A066671 From _Amiram Eldar_, Jul 18 2024: (Start)
%F A066671 a(n) = A069177(A066669(n)).
%F A066671 a(n) = 2^A066672(n). (End)
%e A066671 The first, 4th and 15th terms in A066669 are 7, 13 and 35; phi(7) = 2*3, phi(13) = 4*3, phi(35) = 24 = 8*3; the largest powers of 2 are 2, 4 and 8; so a(1) = 2, a(4) = 4, a(15) = 8.
%t A066671 Select[Array[{#1/#2, #2} & @@ {#, 2^IntegerExponent[#, 2]} &@ EulerPhi@ # &, 200], PrimeQ@ First@ # &][[All, -1]] (* _Michael De Vlieger_, Dec 08 2018 *)
%o A066671 (PARI) lista(nn) = {for (n=1, nn, en=eulerphi(n); if (isprime(p=en>>valuation(en, 2)), print1(en/p, ", ")););} \\ _Michel Marcus_, Jan 03 2017
%Y A066671 Cf. A000010, A065966, A066669, A066670, A066672, A066673, A069177.
%K A066671 nonn
%O A066671 1,1
%A A066671 _Labos Elemer_, Dec 18 2001
%E A066671 Name corrected by _Amiram Eldar_, Jul 18 2024