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 A053285 #39 Aug 20 2025 14:50:09
%S A053285 1,2,4,6,16,20,48,84,256,324,800,1364,3840,5460,12544,19800,65536,
%T A053285 87380,186624,349524,986880,1365336,3345408,5592404,16515072,20250000,
%U A053285 52306176,84768120,252645120,351847488,760320000,1431655764,4288266240,5632621632,13628740608
%N A053285 Totient of 2^n+1.
%H A053285 Max Alekseyev, <a href="/A053285/b053285.txt">Table of n, a(n) for n = 0..1128</a> (terms 0..300 from Robert Israel; terms 301..1062 from Amiram Eldar)
%F A053285 a(n) = A000010(A000051(n)).
%e A053285 It is a power of 2 iff n is a Fermat prime.
%p A053285 seq(numtheory:-phi(2^n+1), n=0..50); # _Robert Israel_, Aug 12 2015
%t A053285 Table[EulerPhi[2^n + 1], {n, 35}] (* _Vincenzo Librandi_, Aug 12 2015 *)
%o A053285 (PARI) vector(40, n, eulerphi(2^n+1)) \\ _Michel Marcus_, Aug 12 2015
%o A053285 (Magma) [EulerPhi(2^n+1) : n in [1..40]]; // _Vincenzo Librandi_, Aug 12 2015
%Y A053285 Cf. A000010, A000225, A002587, A000051, A046798, A046799, A049479, A051953, A054992.
%K A053285 nonn
%O A053285 0,2
%A A053285 _Labos Elemer_, Mar 03 2000
%E A053285 a(0)=1 prepended by _Alois P. Heinz_, Aug 12 2015