A060670 Numbers k such that phi(x) = k has exactly 7 solutions.

32, 132, 156, 544, 912, 924, 1012, 1044, 1140, 1452, 1464, 1472, 1476, 1572, 1664, 1764, 2076, 2100, 2232, 2424, 2580, 2624, 2652, 3096, 3248, 3336, 3444, 3660, 3996, 4488, 4776, 4840, 5060, 5316, 5412, 5696, 6504, 6516, 6540, 6612, 6660, 6780, 6996, 7116

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Example

32 = phi(51) = phi(64) = phi(68) = phi(80) = phi(96) = phi(102) = phi(120).

Mathematica

a = Table[ 0, {8000} ]; Do[ p = EulerPhi[ n ]; If[ p < 8001, a[ [ p ] ]++ ], {n, 1, 25000} ]; Select[ Range[ 8000 ], a[ [ # ] ] == 7 & ]

Prog

(PARI) is(n)=sum(i=1, n, eulerphi(i)==n)==7 \\ Charles R Greathouse IV, Mar 03 2014
(PARI) is(k) = invphiNum(k) == 7 \\ Amiram Eldar, Nov 17 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000010.

Number of solutions: A007617 (0), A007366 (2), A007367 (3), A060667 (4), A060668 (5), A060669 (6), this sequence (7), A060671 (8), A060672 (9), A060673 (10), A060674 (11), A060675 (12).

Sequence in context: A153074 A035503 A059210 * A044364 A044745 A297641

Adjacent sequences: A060667 A060668 A060669 * A060671 A060672 A060673

Keyword

nonn

Author

Robert G. Wilson v, Apr 18 2001

Status

approved