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 A087979 #34 Oct 10 2024 17:32:58
%S A087979 1,1,15,14,14,6,6,42,30,42,168,210,210,420,840,20790,20790,9240,9240,
%T A087979 83160,120120,3984120,5165160,43825320,26860680,43825320,1304863560,
%U A087979 569729160,569729160,16522145640,18176198040,563462139240,1140028049160,3844800479520,1255683068640,65361608151840,65361608151840,65361608151840,413956851628320,1241870554884960,1241870554884960
%N A087979 a(n) = Min {x : sigma(x) = phi(n*x), x is not a prime}, least nonprime solutions to sigma(x) = phi(n*x).
%C A087979 If x is prime then by necessity we have x = 3 and n = 4. Hence, except for a(4), this sequence is the same as A256527. - _Max Alekseyev_, Sep 29 2023
%F A087979 For n >= 5, a(n) = A256527(n). - Conjectured by _Manfred Scheucher_, May 28 2015; proved by _Max Alekseyev_, Sep 29 2023
%e A087979 n=4: a(4)=14, sigma(14) = 24 = phi(4*14) = phi(56).
%e A087979 n=5: a(5)=14, sigma(14) = 24 = phi(5*14) = phi(70).
%t A087979 ds[x_, de_] := DivisorSigma[1, x]-EulerPhi[de*x] a[n_] := Block[{m=1, s=ds[m, n]}, While[(s !=0||PrimeQ[m])&&!Greater[m, 4000000], m++ ]; m]; Table[a[n], {n, 22}]
%Y A087979 Cf. A074891, A000203, A000010, A088830, A256527.
%K A087979 nonn
%O A087979 1,3
%A A087979 _Labos Elemer_, Sep 29 2003
%E A087979 More terms from _David Wasserman_, Jun 20 2005
%E A087979 a(26)-a(31) from _Donovan Johnson_, Feb 06 2010
%E A087979 a(32)-a(34) from _Donovan Johnson_ confirmed, a(35) added by _Giovanni Resta_, May 24 2016
%E A087979 a(36)-a(41) from _Max Alekseyev_, Oct 10 2024