A366608 - OEIS

%I #19 Jan 08 2024 21:00:10

%S 1,4,16,48,256,800,3840,12544,65536,186624,986880,3345408,16515072,

%T 52306176,252645120,760320000,4288266240,13628740608,64258375680,

%U 218462552064,1095233372160,3105655160832,16510446886912,56000724240384,280012271910912,869940000000000

%N a(n) = phi(4^n+1), where phi is Euler's totient function (A000010).

%H Max Alekseyev, <a href="/A366608/b366608.txt">Table of n, a(n) for n = 0..561</a>

%F a(n) = A053285(2*n). - _Max Alekseyev_, Jan 08 2024

%t EulerPhi[4^Range[0,30]+1] (* _Paolo Xausa_, Oct 14 2023 *)

%o (PARI) {a(n) = eulerphi(4^n+1)}

%o (Python)

%o from sympy import totient

%o def A366608(n): return totient((1<<(n<<1))+1) # _Chai Wah Wu_, Oct 14 2023

%Y Cf. A000010, A052539, A057940, A274903, A295501, A366605, A366606, A366607, A366609.

%Y Cf. A053285, A366579, A366618, A366630, A366639, A366658, A366667, A366669, A366690, A366716.

%K nonn

%O 0,2

%A _Sean A. Irvine_, Oct 14 2023