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 A295501 #39 Mar 15 2025 14:08:41
%S A295501 2,8,36,128,600,1728,10584,32768,139968,480000,2640704,6635520,
%T A295501 44717400,132765696,534600000,2147483648,11452896600,26121388032,
%U A295501 183250539864,473702400000,2427720325632,8834232287232,45914084232320,109586090557440,656100000000000
%N A295501 a(n) = phi(4^n-1), where phi is Euler's totient function (A000010).
%H A295501 Max Alekseyev, <a href="/A295501/b295501.txt">Table of n, a(n) for n = 1..1128</a>
%H A295501 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%H A295501 Wikipedia, <a href="http://en.wikipedia.org/wiki/Euler%27s_phi_function">Euler's totient function</a>.
%F A295501 a(n) = n*A027695(n).
%F A295501 a(n) = A053287(2*n) = A053285(n) * A053287(n). - _Max Alekseyev_, Jan 07 2024
%t A295501 EulerPhi[4^Range[30] - 1] (* _Paolo Xausa_, Jun 17 2024 *)
%o A295501 (PARI) {a(n) = eulerphi(4^n-1)}
%Y A295501 Cf. A000010, A053285.
%Y A295501 phi(k^n-1): A053287 (k=2), A295500 (k=3), this sequence (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).
%Y A295501 Cf. A366602, A366603, A366604, A366608.
%K A295501 nonn
%O A295501 1,1
%A A295501 _Seiichi Manyama_, Nov 22 2017