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%I #29 Jan 05 2024 16:57:59
%S 1,2,4,6,16,20,48,84,256,324,800,1364,3840,5460,12544,19800,65536,
%T 87380,186624,349524,986880,1365336,3345408,5592404,16515072,20250000,
%U 52306176,84768120,252645120,351847488,760320000,1431655764,4288266240
%N Totient of 2^n+1.
%H Max Alekseyev, <a href="/A053285/b053285.txt">Table of n, a(n) for n = 0..1122</a> (terms 0..300 from Robert Israel; terms 301..1062 from Amiram Eldar)
%F a(n) = A000010(A000051(n)).
%e It is a power of 2 iff n is a Fermat prime.
%p seq(numtheory:-phi(2^n+1), n=0..50); # _Robert Israel_, Aug 12 2015
%t Table[EulerPhi[2^n + 1], {n, 35}] (* _Vincenzo Librandi_, Aug 12 2015 *)
%o (PARI) vector(40, n, eulerphi(2^n+1)) \\ _Michel Marcus_, Aug 12 2015
%o (Magma) [EulerPhi(2^n+1) : n in [1..40]]; // _Vincenzo Librandi_, Aug 12 2015
%Y Cf. A000010, A000225, A002587, A000051, A046798, A046799, A049479, A051953, A054992.
%K nonn
%O 0,2
%A _Labos Elemer_, Mar 03 2000
%E a(0)=1 prepended by _Alois P. Heinz_, Aug 12 2015