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 A291258 #11 Aug 21 2017 19:14:49
%S A291258 1,2,12,75960,17156160
%N A291258 a(n) is the smallest number k such that sigma(k) - phi(k) = n*k, or 0 if no such k exists.
%C A291258 a(5) and following terms > 10^13, if they exist. - _Giovanni Resta_, Aug 21 2017
%e A291258 a(2) = 12 because sigma(12) = 28, phi(12) = 4; sigma(12) - phi(12) = 2*12 and 12 is the smallest number with this property.
%o A291258 (PARI) a(n) = {my(k=1); while (sigma(k)-eulerphi(k)!=n*k, k++); k; }
%Y A291258 Cf. A000010, A000203, A055681.
%K A291258 nonn,more
%O A291258 0,2
%A A291258 _Altug Alkan_, Aug 21 2017