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A069069 Numbers n such that n*phi(n-1) is a perfect square. 1

%I

%S 9,27,45,49,64,486,637,867,961,1035,1352,1408,1521,3971,4913,7581,

%T 8750,12936,14283,19602,20825,23104,36481,43681,44506,48600,49005,

%U 58621,63001,72897,75843,85697,90168,97470,108241,122317,127008

%N Numbers n such that n*phi(n-1) is a perfect square.

%H Charles R Greathouse IV, <a href="/A069069/b069069.txt">Table of n, a(n) for n = 1..1000</a>

%t Rest[Select[Range[130000],IntegerQ[Sqrt[# EulerPhi[#-1]]]&]] (* _Harvey P. Dale_, Jun 08 2013 *)

%o (PARI) is(n)=issquare(eulerphi(n-1)*n) \\ _Charles R Greathouse IV_, Sep 21 2016

%K nonn

%O 1,1

%A _Benoit Cloitre_, Apr 05 2002

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Last modified February 16 21:46 EST 2020. Contains 331975 sequences. (Running on oeis4.)