A060668 Numbers n such that phi(x) = n has exactly 5 solutions.

8, 20, 220, 272, 300, 368, 416, 456, 500, 656, 732, 848, 876, 1092, 1160, 1212, 1236, 1328, 1376, 1424, 1568, 1624, 1716, 1808, 2144, 2244, 2336, 2420, 2460, 2480, 2528, 2556, 2768, 3056, 3080, 3252, 3320, 3344, 3536, 3560, 3612, 3728, 3732, 3900, 4016

Offset

1,1

Links

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

Example

8 = phi(15) = phi(16) = phi(20) = phi(24) = phi(30).

Mathematica

a = Table[ 0, {5000} ]; Do[ p = EulerPhi[ n ]; If[ p < 5001, a[[ p ]]++ ], {n, 1, 15000} ]; Select[ Range[ 5000 ], a[[ # ]] == 5 & ]

Prog

(PARI) is(n)=sum(k=1, n, eulerphi(k)==n)==5 \\ Charles R Greathouse IV, Mar 03 2014

Crossrefs

Cf. A007366, A007367.

Sequence in context: A208084 A214905 A230987 * A221067 A217018 A108235

Adjacent sequences: A060665 A060666 A060667 * A060669 A060670 A060671

Keyword

nonn

Author

Robert G. Wilson v, Apr 18 2001

Status

approved