$16 、  A$ nine-digit number contains the digits $1, 2, 3, 4, 5, 6, 7, 8, 9$ exactly once, and any two adjacent digits in this nine-digit number can form a two-digit number that can be expressed as the product of two single-digit numbers. This nine-digit number is $\qquad$ -.
【Analysis】Since $9 \times 9=81$, the product of two single-digit numbers cannot represent a number greater than 81, so in this nine-digit number, there cannot be any digit after 9, which means the digit 9 must be in the units place, and the digit 8 must be followed by 1.
Since $8 \times 9=72$, and $7 \times 9=63<70, 8 \times 8=64<70$, the digit 7 must be followed by 2. Since 17, 37, 47, 67 are all prime numbers, $57=3 \times 19, 77=7 \times 11$, 17, 37, 47, 57, 67, 77 cannot be expressed as the product of two single-digit numbers, and 2 must follow 7, so 27 cannot appear, which means there cannot be any digit before 7, so the digit 7 must be in the first place. Since 19, 29, 59, 79 are all prime numbers, and $39=3 \times 13, 69=3 \times 23$, 19, 29, 39, 59, 69, 79 cannot be expressed as the product of two single-digit numbers, so the digit before 9 must be 4. Since $38=2 \times 19, 58=2 \times 29, 68=2^2 \times 17, 18, 48, 78$ cannot appear, the digit before 8 must be 2.
Therefore, this nine-digit number must start with 7281 and end with 49.
Among the remaining 3, 5, 6, both 5 and 6 can follow 1.
If 1 is followed by 5, then 3 cannot follow 5, so 5 must be followed by 6, and 6 must be followed by 3, but $34=2 \times 17$ does not meet the requirement.

Therefore, 1 must be followed by 6, at this point 5 cannot follow 6, so 6 must be followed by 3, and 3 must be followed by 5, the entire nine-digit number is 728163549, which is verified to meet the requirement.
In summary, the required nine-digit number is 728163549.