a(n) = least primitive factor of 2^(2n+1) - 1.

Terms

a(0) =1a(1) =7a(2) =31a(3) =127a(4) =73a(5) =23a(6) =8191a(7) =151a(8) =131071a(9) =524287a(10) =337a(11) =47a(12) =601a(13) =262657a(14) =233a(15) =2147483647a(16) =599479a(17) =71a(18) =223a(19) =79a(20) =13367a(21) =431a(22) =631a(23) =2351a(25) =103a(26) =6361a(27) =881a(28) =32377a(29) =179951a(31) =92737