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 A078557 #16 Feb 24 2025 02:03:38
%S A078557 1,2,3,6,14,15,30,35,42,70,78,105,190,210,357,418,570,714,910,1045,
%T A078557 1254,2090,2730,3135,4522,4674,5278,6270,10659,12441,13566,14630,
%U A078557 15834,16770,20026,21318,23374,24871,24882,24969,25070,25714,27170,29029,33915,35074
%N A078557 Squarefree balanced numbers (i.e., squarefree members of A020492).
%H A078557 Donovan Johnson, <a href="/A078557/b078557.txt">Table of n, a(n) for n = 1..10000</a>
%e A078557 210 = 2*3*5*7, sigma(210) = 576, phi(210) = 48, 576/48 = 12.
%t A078557 Do[s=DivisorSigma[1, n]/EulerPhi[n]; If[IntegerQ[s]&&!Equal[MoebiusMu[n], 0], k=k+1; Print[n]], {n, 1, 2100000}]
%o A078557 (PARI) isok(k) = {my(f = factor(k)); issquarefree(f) && denominator(prod(i = 1, #f~, (f[i, 1]+1)/(f[i, 1]-1))) == 1;} \\ _Amiram Eldar_, Feb 24 2025
%Y A078557 Intersection of A005117 and A020492.
%K A078557 nonn
%O A078557 1,2
%A A078557 _Labos Elemer_, Dec 06 2002