a(n) = gpf(lpf(2^prime(n) - 1) - 1) where prime(n) is the n-th prime.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =11a(5) =13a(6) =257a(7) =73a(8) =23a(9) =29a(10) =331a(11) =37a(12) =163a(13) =43a(14) =47a(15) =53a(16) =61a(17) =1321a(18) =2677a(19) =1609a(20) =73a(21) =79a(22) =83a(23) =2931542417a(24) =97a(25) =278557a(26) =599a(28) =31981a(29) =113a(30) =77158673929