A055688 Numbers k such that 5^k == -1 (mod k-1).

2, 3, 7, 14, 15, 175, 855, 2695, 78127, 103974, 106695, 121975, 420210, 487375, 1299375, 2174655, 3895095, 4151455, 5842215, 5951130, 6508335, 10637055, 20117895, 24482958, 31999695, 32282054, 32620203, 32872455, 34258455

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A055685, A055686, A055687, A055689, A055690, A055691, A055692, A055693, A055694, A055695.

Programs

Mathematica

Do[If[PowerMod[5, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]
Select[Range[2,35*10^6],PowerMod[5,#,#-1]==#-2&] (* Harvey P. Dale, Aug 13 2024 *)

Extensions

a(22) corrected by Amiram Eldar, Jul 23 2021