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 A090779 #17 Aug 20 2021 22:50:02 %S A090779 1,4,8,9,16,18,25,27,32,36,49,50,54,64,72,81,98,100,108,121,125,128, %T A090779 144,147,162,169,196,200,216,225,242,243,250,256,288,289,294,324,338, %U A090779 343,361,392,400,432,441,450,484,486,500,507,512,529,576,578,588,605,625 %N A090779 Numbers k that divide phi(k)^2. %C A090779 Coincides with A073539 in the first 850000 terms and possibly more. - _R. J. Mathar_, Sep 08 2008 %H A090779 Vaclav Kotesovec, <a href="/A090779/b090779.txt">Table of n, a(n) for n = 1..20000</a> %H A090779 Vaclav Kotesovec, <a href="/A090779/a090779.jpg">Plot of a(n)/n^2 and a(n)/(n^2/log(n)) for n = 1..20000</a> %F A090779 a(n) seems to be asymptotic to c*n^2 with c = 0.1.... %t A090779 Select[Range[1000], Divisible[EulerPhi[#]^2,#]&] (* _Vaclav Kotesovec_, Feb 16 2019 *) %K A090779 nonn %O A090779 1,2 %A A090779 _Benoit Cloitre_, Feb 08 2004