Start with 1, then alternately add 2 or double.

Terms

a(0) =1a(1) =3a(2) =6a(3) =8a(4) =16a(5) =18a(6) =36a(7) =38a(8) =76a(9) =78a(10) =156a(11) =158a(12) =316a(13) =318a(14) =636a(15) =638a(16) =1276a(17) =1278a(18) =2556a(19) =2558a(20) =5116a(21) =5118a(22) =10236a(23) =10238a(24) =20476a(25) =20478a(26) =40956a(27) =40958a(28) =81916a(29) =81918