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 A366623 #17 Apr 15 2025 22:23:02
%S A366623 4,24,168,864,6200,30240,223944,1119744,7457184,37200000,277618528,
%T A366623 1254113280,10445497920,51618196224,365601600000,1770091315200,
%U A366623 13439285266176,62336092492800,484935499902880,2179146240000000,17141125020596640,86330728271779200
%N A366623 a(n) = phi(6^n-1), where phi is Euler's totient function (A000010).
%H A366623 Max Alekseyev, <a href="/A366623/b366623.txt">Table of n, a(n) for n = 1..430</a>
%F A366623 a(n) = A000010(A024062(n)). - _Paul F. Marrero Romero_, Oct 23 2023
%t A366623 EulerPhi[6^Range[22] - 1] (* _Paul F. Marrero Romero_, Oct 23 2023 *)
%o A366623 (PARI) {a(n) = eulerphi(6^n-1)}
%Y A366623 phi(k^n-1): A053287 (k=2), A295500 (k=3), A295501 (k=4), A295502 (k=5), this sequence (k=6), A366635 (k=7), A366654 (k=8), A366663 (k=9), A295503 (k=10), A366685 (k=11), A366711 (k=12).
%Y A366623 Cf. A024062, A000010, A295502, A366620, A366621, A366622.
%K A366623 nonn
%O A366623 1,1
%A A366623 _Sean A. Irvine_, Oct 14 2023