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 A366608 #22 Mar 15 2025 14:14:12
%S A366608 1,4,16,48,256,800,3840,12544,65536,186624,986880,3345408,16515072,
%T A366608 52306176,252645120,760320000,4288266240,13628740608,64258375680,
%U A366608 218462552064,1095233372160,3105655160832,16510446886912,56000724240384,280012271910912,869940000000000
%N A366608 a(n) = phi(4^n+1), where phi is Euler's totient function (A000010).
%H A366608 Max Alekseyev, <a href="/A366608/b366608.txt">Table of n, a(n) for n = 0..583</a>
%F A366608 a(n) = A053285(2*n). - _Max Alekseyev_, Jan 08 2024
%t A366608 EulerPhi[4^Range[0,30]+1] (* _Paolo Xausa_, Oct 14 2023 *)
%o A366608 (PARI) {a(n) = eulerphi(4^n+1)}
%o A366608 (Python)
%o A366608 from sympy import totient
%o A366608 def A366608(n): return totient((1<<(n<<1))+1) # _Chai Wah Wu_, Oct 14 2023
%Y A366608 Cf. A000010, A052539, A057940, A274903, A295501, A366605, A366606, A366607, A366609.
%Y A366608 Cf. A053285, A366579, A366618, A366630, A366639, A366658, A366667, A366669, A366690, A366716.
%K A366608 nonn
%O A366608 0,2
%A A366608 _Sean A. Irvine_, Oct 14 2023