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 A366667 #18 Feb 28 2024 13:21:08
%S A366667 1,4,40,288,3072,23600,259200,1847104,21523360,152845056,1700870400,
%T A366667 12550120000,130459631616,997562438080,11159367815680,81159501312000,
%U A366667 926510094425920,6670865700716544,73205598106368000,540340585126398016,5691215305506816000
%N A366667 a(n) = phi(9^n+1), where phi is Euler's totient function (A000010).
%H A366667 Max Alekseyev, <a href="/A366667/b366667.txt">Table of n, a(n) for n = 0..345</a>
%F A366667 a(n) = A000010(A062396(n)). - _Paul F. Marrero Romero_, Nov 04 2023
%F A366667 a(n) = A366579(2*n). - _Max Alekseyev_, Jan 08 2024
%t A366667 EulerPhi[9^Range[0, 20] + 1] (* _Paul F. Marrero Romero_, Nov 04 2023 *)
%o A366667 (PARI) {a(n) = eulerphi(9^n+1)}
%Y A366667 Cf. A062396, A000010, A366663, A366664, A366665, A366666.
%Y A366667 Cf. A053285, A366579, A366608, A366618, A366630, A366639, A366658, A366669, A366690, A366716.
%K A366667 nonn
%O A366667 0,2
%A A366667 _Sean A. Irvine_, Oct 15 2023