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 A356485 #11 Feb 16 2025 08:34:03
%S A356485 1,3,13,64,416,2736,23472,207936,2113344,22584960,284722560,
%T A356485 3576337920,52240412160,768727895040,12228344755200,206114911027200,
%U A356485 3838718125670400,71231050830643200,1468632692485324800,30345814652977152000,666456931810639872000,15172961921551171584000
%N A356485 a(n) = n! * Sum_{k=1..n} A000010(k)/k.
%H A356485 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%F A356485 a(n) ~ n! * 6*n/Pi^2.
%t A356485 Table[n! * Sum[EulerPhi[k]/k, {k, 1, n}], {n, 1, 25}]
%o A356485 (PARI) a(n) = n!*sum(k=1, n, eulerphi(k)/k); \\ _Michel Marcus_, Aug 09 2022
%Y A356485 Cf. A000010, A002088, A011755, A356297, A356010, A356298, A356323.
%K A356485 nonn
%O A356485 1,2
%A A356485 _Vaclav Kotesovec_, Aug 09 2022