a(n) = 2^n - A000031(n).

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =10a(5) =24a(6) =50a(7) =108a(8) =220a(9) =452a(10) =916a(11) =1860a(12) =3744a(13) =7560a(14) =15202a(15) =30576a(16) =61420a(17) =123360a(18) =247542a(19) =496692a(20) =996088a(21) =1997272a(22) =4003558a(23) =8023884a(24) =16077964a(25) =32212248a(26) =64527436a(27) =129246660a(28) =258847876a(29) =518358120