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A067143 Numbers n such that phi(n+1)=3*phi(n). 5
6, 12, 18, 36, 72, 90, 96, 108, 162, 192, 432, 486, 576, 702, 768, 792, 924, 1152, 1296, 1458, 2592, 2916, 3456, 3888, 4698, 5550, 6696, 7998, 8700, 10368, 10590, 11802, 12288, 16470, 17496, 18432, 33250, 39366, 52488, 56790, 79248, 124356 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

MATHEMATICA

Position[Partition[EulerPhi[Range[125000]], 2, 1], _?(#[[2]]==3#[[1]]&), 1, Heads-> False]//Flatten (* Harvey P. Dale, Jul 30 2020 *)

PROG

(PARI) isok(n) = eulerphi(n+1) == 3*eulerphi(n); \\ Michel Marcus, Nov 20 2013

CROSSREFS

Cf. A001274, A050472, A172314.

Sequence in context: A213360 A176682 A226640 * A206038 A205859 A288794

Adjacent sequences: A067140 A067141 A067142 * A067144 A067145 A067146

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 19 2002

EXTENSIONS

More terms from Dean Hickerson, Feb 20 2002

STATUS

approved

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Last modified February 5 03:48 EST 2023. Contains 360082 sequences. (Running on oeis4.)