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 A366618 #9 Jun 07 2025 14:51:14
%S A366618 1,2,12,36,312,1040,7200,25088,183808,557928,4396800,15333120,
%T A366618 121680000,406812744,2817007200,8558784000,76264519680,254230063200,
%U A366618 1710194342400,6349120596480,47334145996800,127169887444992,1088029470747648,3889097389599864
%N A366618 a(n) = phi(5^n+1), where phi is Euler's totient function (A000010).
%H A366618 Max Alekseyev, <a href="/A366618/b366618.txt">Table of n, a(n) for n = 0..471</a>
%t A366618 EulerPhi[5^Range[0,30]+1] (* _Harvey P. Dale_, Jun 07 2025 *)
%o A366618 (PARI) {a(n) = eulerphi(5^n+1)}
%Y A366618 Cf. A000010, A034474, A057939, A074478, A295502, A366615, A366616, A366617.
%Y A366618 Cf. A053285, A366579, A366608, A366630, A366639, A366658, A366667, A366669, A366690, A366716.
%K A366618 nonn
%O A366618 0,2
%A A366618 _Sean A. Irvine_, Oct 14 2023