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A090779 Numbers n such that n divides phi(n)^2. 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Coincides with A073539 in the first 850000 entries and possibly more. [From 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

FORMULA

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

MATHEMATICA

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

CROSSREFS

Sequence in context: A070003 A325661 A073539 * A166402 A255586 A034038

Adjacent sequences:  A090776 A090777 A090778 * A090780 A090781 A090782

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 08 2004

STATUS

approved

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Last modified August 5 22:11 EDT 2020. Contains 336214 sequences. (Running on oeis4.)