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 A020493 #20 Apr 13 2024 05:19:36
%S A020493 1,3,15,30,35,56,70,78,105,140,168,190,210,248,264,357,420,570,616,
%T A020493 630,714,744,812,840,910,1045,1240,1485,1672,1848,2090,2214,2436,2580,
%U A020493 2730,3080,3135,3339,3596,3720,3956,4064,4180,4522,4674,5016,5049,5278,5396
%N A020493 Numbers k such that d(k) (number of divisors) divides phi(k) (Euler function) divides sigma(k) (sum of divisors).
%C A020493 Numbers k such that sigma_0(k) divides phi(k) divides sigma_1(k).
%D A020493 David Wells, Curious and interesting numbers, Penguin Books, p. 130.
%H A020493 Donovan Johnson, <a href="/A020493/b020493.txt">Table of n, a(n) for n = 1..10000</a>
%e A020493 210 has 16 divisors, which divides phi(210) = 48, which in turn divides sigma(210) = 576, so 210 is a term of the sequence.
%t A020493 q[n_] := And @@ IntegerQ /@ Ratios @ {DivisorSigma[0, n], EulerPhi[n], DivisorSigma[1, n]}; Select[Range[6000], q] (* _Amiram Eldar_, Apr 13 2024 *)
%o A020493 (PARI) for(n=1, 1e3, if(sigma(n)%eulerphi(n)==0, if(sigma(n)%numdiv(n)==0, if(eulerphi(n)%numdiv(n)==0, print1(n, ", "))))) \\ _Felix Fröhlich_, Aug 08 2014
%Y A020493 Cf. A000005, A000010, A000203.
%Y A020493 Intersection of A020491 and A020492.
%K A020493 nonn
%O A020493 1,2
%A A020493 _David W. Wilson_
%E A020493 Wells incorrectly has 52 instead of 56.