Smallest prime of form 2^n*k + 1.

Terms

a(0) =2a(1) =3a(2) =5a(3) =17a(4) =17a(5) =97a(6) =193a(7) =257a(8) =257a(9) =7681a(10) =12289a(11) =12289a(12) =12289a(13) =40961a(14) =65537a(15) =65537a(16) =65537a(17) =786433a(18) =786433a(19) =5767169a(20) =7340033a(21) =23068673a(22) =104857601a(23) =167772161a(24) =167772161a(25) =167772161a(26) =469762049a(27) =2013265921a(28) =3221225473a(29) =3221225473