A055692 Numbers k such that 9^k == -1 (mod k-1).

2, 3, 11, 42, 147, 13818, 21450, 27594, 41370, 55011, 126291, 265722, 417123, 1315635, 3994571, 5704611, 6860490, 9298842, 13941354, 14349027, 17658578, 20382810, 26557874, 27841338, 69831363, 86550090, 113272170, 130457571, 163013235, 192688650, 211142538, 333792522

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Crossrefs

Cf. A001019.

Programs

Mathematica

Do[If[PowerMod[9, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]

PARI

isok(k) = Mod(9, k-1)^k == -1; \\ Michel Marcus, Jul 12 2021