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 A090778 #17 Sep 19 2019 11:02:17
%S A090778 1,2,4,6,8,10,12,16,18,20,24,32,36,40,42,48,50,54,60,64,72,80,84,96,
%T A090778 100,108,114,120,126,128,136,144,156,160,162,168,180,192,200,216,220,
%U A090778 228,240,250,252,256,272,288,294,300,312,320,324,336,342,360,378,384,400
%N A090778 Numbers k such that phi(k) divides k*(k - phi(k)).
%C A090778 Also phi(k) divides k^2. - _Enrique Pérez Herrero_, Jul 04 2010
%H A090778 Amiram Eldar, <a href="/A090778/b090778.txt">Table of n, a(n) for n = 1..10000</a>
%F A090778 a(n) seems to be asymptotic to c*n^2 with c=0.11.....
%t A090778 pdnQ[n_]:=Module[{ephi=EulerPhi[n]},Divisible[n(n-ephi),ephi]]; Select[ Range[ 400],pdnQ] (* _Harvey P. Dale_, Dec 22 2015 *)
%K A090778 nonn
%O A090778 1,2
%A A090778 _Benoit Cloitre_, Feb 08 2004