A060667 - OEIS

A060667

Numbers n such that phi(x) = n has exactly 4 solutions.

4, 6, 18, 42, 100, 162, 184, 208, 328, 424, 460, 468, 486, 492, 616, 636, 664, 688, 700, 712, 784, 820, 900, 904, 1020, 1060, 1072, 1168, 1240, 1264, 1276, 1288, 1300, 1356, 1360, 1384, 1404, 1458, 1480, 1528, 1672, 1740, 1768, 1864, 1896, 1900, 1908, 2008

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OFFSET

1,1

LINKS

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

EXAMPLE

18 = phi(19) = phi(27) = phi(38) = phi(54).

MATHEMATICA

a = Table[ 0, {2500} ]; Do[ p = EulerPhi[ n ]; If[ p < 2501, a[ [ p ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 2500 ], a[ [ # ] ] == 4 & ]

CROSSREFS

Cf. A007366, A007367.

Sequence in context: A303526 A064403 A235344 * A218065 A005959 A057393

Adjacent sequences: A060664 A060665 A060666 * A060668 A060669 A060670

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Apr 18 2001

STATUS

approved