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 A066781 #23 Nov 18 2020 06:52:05
%S A066781 2,2,4,4,16,4,64,16,64,16,1024,16,4096,64,256,256,65536,64,262144,256,
%T A066781 4096,1024,4194304,256,1048576,4096,262144,4096,268435456,256,
%U A066781 1073741824,65536,1048576,65536,16777216,4096,68719476736,262144,16777216,65536
%N A066781 a(n) = 2^phi(n).
%H A066781 Harry J. Smith, <a href="/A066781/b066781.txt">Table of n, a(n) for n = 1..300</a>
%F A066781 From _Amiram Eldar_, Nov 18 2020: (Start)
%F A066781 a(n) = 2^A000010(n).
%F A066781 Sum_{n>=1} 1/a(n) = A334071. (End)
%t A066781 Table[2^EulerPhi[n], {n, 40}] (* _Arkadiusz Wesolowski_, Jan 16 2013 *)
%o A066781 (PARI) a(n) = 2^eulerphi(n); \\ _Harry J. Smith_, Mar 25 2010
%Y A066781 Cf. A000010, A334071.
%K A066781 nonn
%O A066781 1,1
%A A066781 _Benoit Cloitre_, Jan 18 2002