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 A295500 #23 Feb 16 2025 08:33:52
%S A295500 1,4,12,32,110,288,1092,2560,9072,26400,84700,165888,797160,2384928,
%T A295500 6019200,15728640,64533700,141087744,580765248,1246080000,4823425152,
%U A295500 14758128000,46070066188,85996339200,385087175000,1270928131200,3474144608256,8810420097024
%N A295500 a(n) = phi(3^n-1), where phi is Euler's totient function (A000010).
%H A295500 Max Alekseyev, <a href="/A295500/b295500.txt">Table of n, a(n) for n = 1..690</a>
%H A295500 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>
%H A295500 Wikipedia, <a href="http://en.wikipedia.org/wiki/Euler%27s_phi_function">Euler's totient function</a>
%F A295500 a(n) = n*A027385(n).
%F A295500 a(n) = A000010(A024023(n)). - _Michel Marcus_, Jun 18 2024
%t A295500 EulerPhi[3^Range[30] - 1] (* _Paolo Xausa_, Jun 18 2024 *)
%o A295500 (PARI) {a(n) = eulerphi(3^n-1)}
%Y A295500 Cf. A000010, A024023, A027385.
%Y A295500 phi(k^n-1): A053287 (k=2), this sequence (k=3), A295501 (k=4), A295502 (k=5), A366623 (k=6), A366635 (k=7), A366654 (k=8), A366663 (k=9), A295503 (k=10), A366685 (k=11), A366711 (k=12).
%K A295500 nonn
%O A295500 1,2
%A A295500 _Seiichi Manyama_, Nov 22 2017