The binary expansion of a(n) is the first n terms of 2 - A000002.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =9a(5) =19a(6) =38a(7) =77a(8) =154a(9) =308a(10) =617a(11) =1234a(12) =2468a(13) =4937a(14) =9875a(15) =19750a(16) =39501a(17) =79003a(18) =158006a(19) =316012a(20) =632025a(21) =1264050a(22) =2528101a(23) =5056203a(24) =10112406a(25) =20224813a(26) =40449626a(27) =80899252a(28) =161798505a(29) =323597011