Duplicate of A014234.

Terms

a(0) =3a(1) =7a(2) =13a(3) =31a(4) =61a(5) =127a(6) =251a(7) =509a(8) =1021a(9) =2039a(10) =4093a(11) =8191a(12) =16381a(13) =32749