Primes of the form 2^r * 17^s - 1.

Terms

a(0) =3a(1) =7a(2) =31a(3) =67a(4) =127a(5) =271a(6) =577a(7) =1087a(8) =2311a(9) =8191a(10) =78607a(11) =131071a(12) =524287a(13) =1114111a(14) =2367487a(15) =2672671a(16) =17825791a(17) =42762751a(18) =90870847a(19) =606076927a(20) =2147483647a(21) =5151653887a(22) =5815734271a(23) =9697230847a(24) =329705848831a(25) =474351505987a(26) =700624928767a(27) =892896952447