%I #11 Jul 11 2021 15:32:55
%S 2,102,41310,102690,309162,315150,1000002,2488530,4564350,12679002,
%T 17166870,28855610,35049930,38982870,42176490,43232070,53288510,
%U 64253070,104439090,126446850,130659210,144379602,208313490,252852390,284335410,284397750,337122750,379257930,385659630
%N Numbers k such that 10^k == -1 (mod k-1).
%t Do[If[PowerMod[10, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Jun 09 2000
%E Corrected and extended by _Max Alekseyev_, Oct 12 2012