A055687 Numbers k such that 4^k == -1 (mod k-1).

2, 18, 4098, 7362, 85074, 658530, 3999138, 72281282, 285143058, 628944690, 854112114, 1423081170, 2561019282, 3111576930, 4298117634, 5921265042, 14224884930, 21336998130, 34317377234, 50723421714, 63797137890, 144269032050, 163834314354, 187397322210, 212565453282, 231286579794, 232992827298, 266198715090, 314834584482, 348160787730, 580045717650, 706501722498

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Programs

Mathematica

Do[If[PowerMod[4, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]

Extensions

Terms a(9) onward from Max Alekseyev, Oct 12 2012