A060673 - OEIS

A060673

Numbers n such that phi(x) = n has exactly 10 solutions.

24, 80, 180, 256, 264, 828, 1188, 1640, 1968, 2024, 2368, 2544, 2720, 2772, 2904, 3036, 3136, 3144, 3328, 3392, 3420, 4192, 4392, 4464, 4600, 5000, 5312, 5504, 5508, 5688, 5728, 5796, 5800, 6208, 6228, 6732, 6888, 7000, 7232, 7740, 7956, 8388, 8576, 9088

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OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

EXAMPLE

24 = phi(35) = phi(39) = phi(45) = phi(52) = phi(56) = phi(70) = phi(72) = phi(78) = phi(84) = phi(90).

MATHEMATICA

a = Table[ 0, {10000} ]; Do[ p = EulerPhi[ n ]; If[ p < 10001, a[ [ p ] ]++ ], {n, 1, 35000} ]; Select[ Range[ 10000 ], a[ [ # ] ] == 10 & ]

Take[Select[Tally[EulerPhi[Range[50000]]], #[[2]]==10&][[;; , 1]]//Union, 50] (* Harvey P. Dale, Sep 15 2023 *)

PROG

(PARI) is(n)=sum(i=1, n, eulerphi(i)==n)==10 \\ Charles R Greathouse IV, Mar 03 2014

CROSSREFS

Cf. A007366, A007367.

Sequence in context: A143839 A114818 A190102 * A167561 A211575 A211583

Adjacent sequences: A060670 A060671 A060672 * A060674 A060675 A060676

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Apr 18 2001

STATUS

approved