Largest primitive prime factor of 2^n-1, or a(n) = 1 if no such prime exists.

Terms

a(0) =1a(1) =3a(2) =7a(3) =5a(4) =31a(5) =1a(6) =127a(7) =17a(8) =73a(9) =11a(10) =89a(11) =13a(12) =8191a(13) =43a(14) =151a(15) =257a(16) =131071a(17) =19a(18) =524287a(19) =41a(20) =337a(21) =683a(22) =178481a(23) =241a(24) =1801a(25) =2731a(26) =262657a(27) =113a(28) =2089a(29) =331