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 A135240 #7 Sep 13 2018 09:31:36
%S A135240 36,20575296
%N A135240 Numbers n such that phi(sigma(n))=2n.
%C A135240 No other terms below 10^10. - _Max Alekseyev_, Sep 25 2009
%C A135240 6.5*10^12 < a(3) <= 180577942272000000. We also have phi(sigma(n)) = 3*n for n = 144982963520227123200 and phi(sigma(n)) = 4*n for n = 16310583396025551360000 thus these may not be the smallest such n. - _Giovanni Resta_, Sep 13 2018
%e A135240 phi(sigma(20575296))=phi(71238999)=41150592=2*20575296, so 20575296 is in the sequence.
%t A135240 Do[If[EulerPhi[DivisorSigma[1,n]]==2n,Print[n]],{n,350000000}]
%Y A135240 Cf. A071525, A135238, A135239.
%K A135240 bref,more,nonn
%O A135240 1,1
%A A135240 _Farideh Firoozbakht_, Dec 26 2007