Duplicate of A077835.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =52a(5) =152a(6) =444a(7) =1296a(8) =3784a(9) =11048a(10) =32256a(11) =94176a(12) =274960a(13) =802784a(14) =2343840