A090779 Numbers k that divide phi(k)^2.

1, 4, 8, 9, 16, 18, 25, 27, 32, 36, 49, 50, 54, 64, 72, 81, 98, 100, 108, 121, 125, 128, 144, 147, 162, 169, 196, 200, 216, 225, 242, 243, 250, 256, 288, 289, 294, 324, 338, 343, 361, 392, 400, 432, 441, 450, 484, 486, 500, 507, 512, 529, 576, 578, 588, 605, 625

Offset: 1

Author

Benoit Cloitre, Feb 08 2004

Keywords

• nonn

Comments

Coincides with A073539 in the first 850000 terms and possibly more. - R. J. Mathar, Sep 08 2008

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 1..20000
• Vaclav Kotesovec, Plot of a(n)/n^2 and a(n)/(n^2/log(n)) for n = 1..20000

Programs

Mathematica

Select[Range[1000], Divisible[EulerPhi[#]^2,#]&] (* Vaclav Kotesovec, Feb 16 2019 *)

Formula

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