First n-bit number to appear in Van Eck's sequence (A181391).

Terms

a(0) =0a(1) =2a(2) =6a(3) =9a(4) =17a(5) =42a(6) =92a(7) =131a(8) =307a(9) =650a(10) =1024a(11) =2238a(12) =4164a(13) =8226a(14) =17384a(15) =33197a(16) =67167a(17) =133549a(18) =269119a(19) =525974a(20) =1055175a(21) =2111641a(22) =4213053a(23) =8444257a(24) =16783217a(25) =33601813a(26) =67405064a(27) =134239260a(28) =268711604a(29) =538400994