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 A060609 #8 Aug 23 2025 13:47:33
%S A060609 2,2,4,2,4,4,16,2,4,4,8,4,16,4,4,8,4,16,8,8,8,8,16,16,32,16,32,8,4,16,
%T A060609 4,16,64,8,8,16,16,2,16,8,16,16,8,64,8,16,16,8,16,8,16,32,64,16,256,
%U A060609 16,16,8,16,32,8,16,32,32,32,16,32,32,8,16,64,16,32,32,4,8,64,32,64,128
%N A060609 Repeatedly apply Euler phi to n-th prime; a(n) = highest power of 2 that is seen.
%H A060609 Amiram Eldar, <a href="/A060609/b060609.txt">Table of n, a(n) for n = 1..10000</a>
%F A060609 a(n) = A049116(A000040(n)).
%e A060609 n=100,p(100)=541, Phi-iteration chain is {541,540,144,48,16,8,4,2,1} with 9 terms. The largest power of 2 is the 5th term=16=a(100).
%t A060609 Table[Max[Select[NestWhileList[EulerPhi[#]&,Prime[n],#>1&],IntegerQ[Log2[#]]&]],{n,80}] (* _Harvey P. Dale_, Aug 23 2025 *)
%Y A060609 Cf. A000040, A000010, A049108, A049113, A049116, A003434.
%K A060609 easy,nonn,changed
%O A060609 1,1
%A A060609 _Labos Elemer_, Apr 13 2001