One of the ways to solve this problem is compute $10^x \, mod \, p$ for example for $p = 7$ the sequence of the answers of this expression is:
$[1, 3, 2, 6, 4, 5]$ (sequence of answers is a periodic with this period)
so $6$ should count $n!$
it means $3 \le n$
One of the ways to solve this problem is compute $10^x \, mod \, p$ for example for $p = 7$ the sequence of the answers of this expression is:
$[1, 3, 2, 6, 4, 5]$ (sequence of answers is a periodic with this period)
so $6$ should count $n!$
it means $3 \le n$