A067076 + A000079/2.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =12a(5) =21a(6) =39a(7) =72a(8) =138a(9) =269a(10) =526a(11) =1041a(12) =2067a(13) =4116a(14) =8214a(15) =16409a(16) =32796a(17) =65565a(18) =131104a(19) =262178a(20) =524323a(21) =1048614a(22) =2097192a(23) =4194347a(24) =8388655a(25) =16777265a(26) =33554482a(27) =67108916a(28) =134217781