Duplicate of A023195.

Terms

a(0) =3a(1) =7a(2) =13a(3) =31a(4) =127a(5) =307a(6) =1093a(7) =1723a(8) =2801a(9) =3541a(10) =5113a(11) =8011a(12) =8191a(13) =10303a(14) =17293a(15) =19531