OFFSET
1,1
MATHEMATICA
Do[If[PowerMod[9, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]
PROG
(PARI) isok(k) = Mod(9, k-1)^k == -1; \\ Michel Marcus, Jul 12 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Jun 09 2000
STATUS
approved