Erroneous version of A001679.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =6a(5) =12a(6) =20a(7) =39a(8) =71a(9) =137a(10) =261a(11) =511a(12) =995a(13) =1974a(14) =3915a(15) =7841a(16) =15749a(17) =31835