A067143 Numbers n such that phi(n+1) = 3*phi(n).

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

Offset: 1

Author

Benoit Cloitre, Feb 19 2002

Keywords

• nonn

Links

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

Crossrefs

Cf. A001274, A050472, A172314.

Programs

Mathematica

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

PARI

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

Extensions

More terms from Dean Hickerson, Feb 20 2002