"Primitive" numbers k such that k divides 4^k - 1.

Terms

a(0) =1a(1) =3a(2) =21a(3) =147a(4) =171a(5) =657a(6) =903a(7) =1029a(8) =1197a(9) =2667a(10) =3249a(11) =4599a(12) =6321a(13) =7077a(14) =7203a(15) =8379a(16) =12483a(17) =13203a(18) =18669a(19) =22743a(20) =32193a(21) =38829a(22) =44247a(23) =47961a(24) =49539a(25) =50421a(26) =51471a(27) =58653a(28) =61731a(29) =71631