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 A335818 #29 Feb 16 2025 08:34:00
%S A335818 2,4,7,6,1,9,4,7,4,8,1,6,5,0,2,5,7,9,4,3,2,6,8,5,5,4,4,4,1,2,5,1,4,5,
%T A335818 1,6,0,0,4,5,4,5,6,8,5,6,3,5,5,2,8,4,3,8,4,3,4,5,7,0,7,8,7,9,1,5,0,9,
%U A335818 4,9,0,3,0,1,1,7,5,1,2,4,5,8,1,7,6,2,8,0,1,3,4,6,1,5,2,6,7,3,8,9,3,3,2,8,9
%N A335818 Decimal expansion of Sum_{k>=1} 1/phi(k)^3, where phi is the Euler totient function.
%C A335818 Sum_{k>=1} 1/phi(k)^m is convergent iff m > 1 (reference Monier). - _Bernard Schott_, Jan 14 2021
%D A335818 Jean-Marie Monier, Analyse, Exercices corrigés, 2ème année MP, Dunod, 1997, Exercice 3.2.21, pp. 281 and 294.
%H A335818 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%H A335818 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientSummatoryFunction.html">Totient Summatory Function</a>.
%H A335818 Wikipedia, <a href="http://en.wikipedia.org/wiki/Euler%27s_phi_function">Euler's totient function</a>.
%F A335818 Equals Product_{primes p} (1 + 1/((1 - 1/p)^3 * (p^3 - 1))).
%e A335818 2.476194748165025794326855444125145160045456856355284384345707879150949...
%t A335818 $MaxExtraPrecision = 1000; f[p_] := (1 + 1/((1 - 1/p)^s * (p^s - 1))) /. s -> 3; Do[cc = Rest[CoefficientList[Series[Log[f[1/x]], {x, 0, m}], x]]; Print[f[2] * Exp[N[Sum[Indexed[cc, n]*(PrimeZetaP[n] - 1/2^n), {n, 2, m}], 120]]], {m, 100, 1000, 100}]
%o A335818 (PARI) prodeulerrat(1 + 1/((1 - 1/p)^3 * (p^3 - 1))) \\ _Amiram Eldar_, Mar 15 2021
%Y A335818 Cf. A000010, A065484, A109695, A335319.
%K A335818 nonn,cons
%O A335818 1,1
%A A335818 _Vaclav Kotesovec_, Jun 25 2020