Binary expansion is 1xx100...0 where xx = 00 or 11.

Terms

a(0) =9a(1) =15a(2) =18a(3) =30a(4) =36a(5) =60a(6) =72a(7) =120a(8) =144a(9) =240a(10) =288a(11) =480a(12) =576a(13) =960a(14) =1152a(15) =1920a(16) =2304a(17) =3840a(18) =4608a(19) =7680a(20) =9216a(21) =15360a(22) =18432a(23) =30720a(24) =36864a(25) =61440a(26) =73728a(27) =122880a(28) =147456a(29) =245760