A094536/2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =5a(5) =10a(6) =22a(7) =44a(8) =91a(9) =182a(10) =370a(11) =740a(12) =1490a(13) =2980a(14) =5980a(15) =11960a(16) =23957a(17) =47914a(18) =95902a(19) =191804a(20) =383750a(21) =767500a(22) =1535284a(23) =3070568a(24) =6141694a(25) =12283388a(26) =24567892a(27) =49135784a(28) =98273780a(29) =196547560