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A069069 Numbers n such that n*phi(n-1) is a perfect square. 1
9, 27, 45, 49, 64, 486, 637, 867, 961, 1035, 1352, 1408, 1521, 3971, 4913, 7581, 8750, 12936, 14283, 19602, 20825, 23104, 36481, 43681, 44506, 48600, 49005, 58621, 63001, 72897, 75843, 85697, 90168, 97470, 108241, 122317, 127008 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..1000

MATHEMATICA

Rest[Select[Range[130000], IntegerQ[Sqrt[# EulerPhi[#-1]]]&]] (* Harvey P. Dale, Jun 08 2013 *)

PROG

(PARI) is(n)=issquare(eulerphi(n-1)*n) \\ Charles R Greathouse IV, Sep 21 2016

CROSSREFS

Sequence in context: A103753 A238333 A103965 * A031088 A020156 A287661

Adjacent sequences:  A069066 A069067 A069068 * A069070 A069071 A069072

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Apr 05 2002

STATUS

approved

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Last modified July 23 22:49 EDT 2019. Contains 325278 sequences. (Running on oeis4.)