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 A053098 #19 Nov 19 2024 01:02:18
%S A053098 2,2,8,16,128,512,8192,16384,262144,2097152,16777216,67108864,
%T A053098 2147483648,8589934592,274877906944,4398046511104,70368744177664,
%U A053098 1125899906842624,18014398509481984,288230376151711744,2305843009213693952,18446744073709551616,1180591620717411303424
%N A053098 When the Euler phi function is iterated with initial value primorial(n) = A002110(n), a(n)= first (maximum) power of 2 emerging during iteration.
%C A053098 Analogous to A053047 (the same with a similar large initial value, n!).
%H A053098 Amiram Eldar, <a href="/A053098/b053098.txt">Table of n, a(n) for n = 1..500</a>
%F A053098 a(n) = 2^A053099(n). - _Amiram Eldar_, Nov 19 2024
%e A053098 For n = 6, A002110(6) = 30030, the corresponding iteration chain is {30030, 5760, 1536, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1}. The first power of 2 is the 4th item after 3 iterations. It is 512, therefore a(6) = 512.
%t A053098 a[n_] := 2^ Max@ IntegerExponent[ FixedPointList[ EulerPhi, Times @@ Prime[Range[n]]], 2]; Array[a, 20] (* _Giovanni Resta_, May 30 2018 *)
%o A053098 (PARI) a(n) = {my(p = prod(i=1, n, prime(i))); while(p >> valuation(p, 2) > 1, p = eulerphi(p)); 1 << valuation(p, 2);} \\ _Amiram Eldar_, Nov 19 2024
%Y A053098 Cf. A000010, A002110, A053047, A053099.
%K A053098 nonn
%O A053098 1,1
%A A053098 _Labos Elemer_, Feb 28 2000
%E A053098 a(21)-a(23) from _Amiram Eldar_, Nov 19 2024