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 A291566 #15 Jun 26 2019 08:11:38
%S A291566 6,30,42,70,105,168,210,420,570,714,744,840,1254,1848,2090,2436,2730,
%T A291566 2970,3135,3720,5016,6270,6678,8680,9240,10098,10788,11868,12180,
%U A291566 12192,12540,13566,14630,15834,16188,20790,21318,24024,24882,25080,25908,26040,26796,32130,43890,48360
%N A291566 Non-primitive balanced numbers: balanced numbers of the form m*n where m, n > 1 are both balanced.
%C A291566 A positive integer, n, is a balanced number (A020492) if sigma(n) is a multiple of phi(n). Since phi and sigma are multiplicative functions, if m and n are balanced numbers and gcd(m,n)=1, mn is also a balanced number. This sequence consists of only these imprimitive terms.
%H A291566 Amiram Eldar, <a href="/A291566/b291566.txt">Table of n, a(n) for n = 1..5000</a>
%e A291566 2 and 3 are balanced numbers, gcd(2,3)=1, so 6 is a non-primitive balanced number.
%t A291566 balQ[n_] := Divisible[DivisorSigma[1,n], EulerPhi[n]]; nonprimQ[n_] := balQ[n] && Module[{d = Divisors[n], ans = False}, Do[If[GCD[d[[k]], n/d[[k]]]==1 && balQ[ d[[k]]] && balQ[n/d[[k]]], ans=True; Break[]], {k, 2, Floor[Length[d]/2]}]; ans]; Select[Range[50000], nonprimQ] (* _Amiram Eldar_, Jun 26 2019 *)
%Y A291566 Cf. A020492, A291565.
%K A291566 nonn
%O A291566 1,1
%A A291566 _Jud McCranie_, Aug 26 2017