Duplicate of A082541.

Terms

a(0) =1a(1) =7a(2) =21a(3) =63a(4) =189a(5) =567a(6) =1701a(7) =5103a(8) =15309a(9) =45927a(10) =137781a(11) =413343a(12) =1240029a(13) =3720087