A068382 Numbers k such that k divides 9^k - 1.

1, 2, 4, 8, 10, 16, 20, 32, 40, 50, 64, 80, 100, 110, 128, 136, 160, 164, 200, 220, 250, 256, 272, 320, 328, 400, 440, 500, 512, 544, 550, 610, 640, 656, 680, 800, 820, 880, 1000, 1024, 1088, 1100, 1210, 1220, 1250, 1280, 1312, 1360, 1544, 1600, 1640, 1760

Offset: 1

Author

Benoit Cloitre, Mar 05 2002

Keywords

• easy
• nonn

Comments

For all m the sequence includes 2^m, 10^m, 2*10^m, 10*2^m.

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A014945, A014946, A014949, A014950.

Programs

Mathematica

Join[{1}, Select[Range[10000], PowerMod[9, #, #] == 1 &]] (* Robert Price, Apr 04 2020 *)

PARI

isok(n) = Mod(9, n)^n == Mod(1, n); \\ Michel Marcus, May 06 2016