A067945 Numbers k that divide 3^k - 1.

1, 2, 4, 8, 16, 20, 32, 40, 64, 80, 100, 128, 160, 200, 220, 256, 272, 320, 328, 400, 440, 500, 512, 544, 640, 656, 800, 880, 1000, 1024, 1088, 1100, 1220, 1280, 1312, 1360, 1600, 1640, 1760, 2000, 2048, 2176, 2200, 2420, 2440, 2500, 2560, 2624, 2720, 3088

Offset: 1

Author

Benoit Cloitre, Mar 05 2002

Keywords

• easy
• nonn

Comments

Closed under multiplication: if x and y are terms then so is x*y.

The number (3^k-1)/2 is a term of this sequence if and only if k is a term. - Thomas Ordowski, Jul 25 2024

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A024023.

Programs

Mathematica

Join[{1},Select[Range[3100],PowerMod[3,#,#]==1&]] (* Harvey P. Dale, Nov 01 2024 *)

PARI

is(n)=Mod(3,n)^n==1 \\ Charles R Greathouse IV, Aug 01 2016