%I

%S 1,7,49,343,2359,2401,16513,16807,115591,117649,794983,809137,823543

%N Numbers n such that n | 4^n + 2^n + 1.

%t Select[ Range[ 10^6 ], Mod[ PowerMod[ 4, #, # ] + PowerMod[ 2, #, # ] + 1, # ] == 0 & ]

%K nonn

%O 1,2

%A _Robert G. Wilson v_, Nov 09 2000