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a(n) = 2^phi(n).
12

%I #23 Nov 18 2020 06:52:05

%S 2,2,4,4,16,4,64,16,64,16,1024,16,4096,64,256,256,65536,64,262144,256,

%T 4096,1024,4194304,256,1048576,4096,262144,4096,268435456,256,

%U 1073741824,65536,1048576,65536,16777216,4096,68719476736,262144,16777216,65536

%N a(n) = 2^phi(n).

%H Harry J. Smith, <a href="/A066781/b066781.txt">Table of n, a(n) for n = 1..300</a>

%F From _Amiram Eldar_, Nov 18 2020: (Start)

%F a(n) = 2^A000010(n).

%F Sum_{n>=1} 1/a(n) = A334071. (End)

%t Table[2^EulerPhi[n], {n, 40}] (* _Arkadiusz Wesolowski_, Jan 16 2013 *)

%o (PARI) a(n) = 2^eulerphi(n); \\ _Harry J. Smith_, Mar 25 2010

%Y Cf. A000010, A334071.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Jan 18 2002