A366608 a(n) = phi(4^n+1), where phi is Euler's totient function (A000010).

1, 4, 16, 48, 256, 800, 3840, 12544, 65536, 186624, 986880, 3345408, 16515072, 52306176, 252645120, 760320000, 4288266240, 13628740608, 64258375680, 218462552064, 1095233372160, 3105655160832, 16510446886912, 56000724240384, 280012271910912, 869940000000000

Offset: 0

Author

Sean A. Irvine, Oct 14 2023

Keywords

• nonn

Links

• Max Alekseyev, Table of n, a(n) for n = 0..583

Crossrefs

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

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

Programs

Mathematica

EulerPhi[4^Range[0,30]+1] (* Paolo Xausa, Oct 14 2023 *)

PARI

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

Python

from sympy import totient
def A366608(n): return totient((1<<(n<<1))+1) # Chai Wah Wu, Oct 14 2023

Formula

a(n) = A053285(2*n). - Max Alekseyev, Jan 08 2024