The number of numbers with n digits is the same as the number of combinations of n things taken from 9. That means as many numbers have 5 or more digits as have 4 or fewer, with the exception that the number 123456789 is not matched by the number 0 (or a number with no digits). There are 256 numbers with 5 or more digits, but only 255 with 4 or fewer.
So, the median number is the first number with 5 digits:
