6. If in the expression $9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1$ some of the “ $\times$ ” are changed to “ $\div$ ” so that the final result is still a natural number, denoted as $N$, then the smallest $N$ is $\qquad$ .
6. If in the expression $9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1$ some of the “$\times$” are changed to “$\div$” so that the final result is still a natural number, denoted as $N$, then the smallest $N$ is $\qquad$.

【Solution】Solution: According to the analysis, first decompose the prime factors $9=3 \times 3, 8=2 \times 2 \times 2, 6=2 \times 3$, hence we have:
$$
\begin{array}{l}
9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1=(3 \times 3) \times(2 \times 2 \times 2) \times 7 \times(3 \times 2) \times 5 \times(2 \times 2) \times 3 \\
\times 2 \times 1,
\end{array}
$$

Therefore, it can be transformed into: $9 \times 8 \times 7 \div 6 \times 5 \div 4 \div 3 \times 2 \times 1=70$, at this point $N$ is the smallest, which is 70, so the answer is: 70.