A060672 - OEIS

A060672

Numbers n such that phi(x) = n has exactly 9 solutions.

40, 60, 108, 128, 252, 276, 440, 612, 696, 996, 1088, 1380, 1500, 1824, 1860, 1932, 2064, 2472, 2796, 2928, 3060, 3132, 3384, 3516, 4584, 4932, 5076, 5136, 5436, 5700, 5888, 6096, 6372, 6640, 6744, 7020, 7080, 7380, 7452, 7476, 7704, 8040, 8676, 8892

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OFFSET

1,1

LINKS

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

EXAMPLE

40 = phi(41) = phi(55) = phi(75) = phi(82) = phi(88) = phi(100) = phi(110) = phi(132) = phi(150).

MATHEMATICA

a = Table[ 0, {10000} ]; Do[ p = EulerPhi[ n ]; If[ p < 10001, a[ [ p ] ]++ ], {n, 1, 35000} ]; Select[ Range[ 10000 ], a[ [ # ] ] == 9 & ]

PROG

(PARI) is(n)=sum(i=1, n, eulerphi(i)==n)==9 \\ Charles R Greathouse IV, Mar 03 2014

CROSSREFS