a(n) = A000225(n+3)-A052955(n).

Terms

a(0) =6a(1) =13a(2) =28a(3) =58a(4) =120a(5) =244a(6) =496a(7) =1000a(8) =2016a(9) =4048a(10) =8128a(11) =16288a(12) =32640a(13) =65344a(14) =130816a(15) =261760a(16) =523776a(17) =1047808a(18) =2096128a(19) =4192768a(20) =8386560a(21) =16774144a(22) =33550336a(23) =67102720a(24) =134209536a(25) =268423168a(26) =536854528a(27) =1073717248a(28) =2147450880