A055689 Numbers k such that 6^k == -1 (mod k-1).

2, 38, 16987850, 2416266950, 5995229030, 7193673830, 11465419550, 17783484530, 72155530502, 142013229530, 174523785590, 189282539138, 294183810998, 302690164298, 354613312130, 774557575610, 933821938790, 1407294504938, 1974020768390, 2112969494570, 2878251281402, 3239815009970, 3756030401750, 3915556797110, 6086837726270, 6154479362702, 6760841132870, 7412805544190, 7430816963570, 10197159330050, 12162461471270, 15374128532210, 15561152727890, 17132853402170, 17728631282570, 25843631671550, 38138222902514, 39974191417010, 56482483860710, 71475592618370, 78107027121482

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Programs

Mathematica

Do[If[PowerMod[6, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]

Extensions

Terms a(4) onward from Max Alekseyev, Oct 12 2012