a(n) = the largest positive multiple of n with exactly n digits when written in binary.

Terms

a(0) =1a(1) =2a(2) =6a(3) =12a(4) =30a(5) =60a(6) =126a(7) =248a(8) =504a(9) =1020a(10) =2046a(11) =4092a(12) =8190a(13) =16380a(14) =32760a(15) =65520a(16) =131070a(17) =262134a(18) =524286a(19) =1048560a(20) =2097144a(21) =4194300a(22) =8388606a(23) =16777200a(24) =33554425a(25) =67108860a(26) =134217702a(27) =268435440a(28) =536870910a(29) =1073741820