A090779 - OEIS

%I #17 Aug 20 2021 22:50:02

%S 1,4,8,9,16,18,25,27,32,36,49,50,54,64,72,81,98,100,108,121,125,128,

%T 144,147,162,169,196,200,216,225,242,243,250,256,288,289,294,324,338,

%U 343,361,392,400,432,441,450,484,486,500,507,512,529,576,578,588,605,625

%N Numbers k that divide phi(k)^2.

%C Coincides with A073539 in the first 850000 terms and possibly more. - _R. J. Mathar_, Sep 08 2008

%H Vaclav Kotesovec, <a href="/A090779/b090779.txt">Table of n, a(n) for n = 1..20000</a>

%H 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 a(n) seems to be asymptotic to c*n^2 with c = 0.1....

%t Select[Range[1000], Divisible[EulerPhi[#]^2,#]&] (* _Vaclav Kotesovec_, Feb 16 2019 *)

%K nonn

%O 1,2

%A _Benoit Cloitre_, Feb 08 2004