Stay button math problem

Only one multiplication factor of 2 and 5 may constitute 0, 2, since the number of factors must be greater than or equal to 5, it is equivalent to the number of seeking factor 5, the number of factors containing 5 has two rules, one bit is 0 or 5 number of factors must contain 5, this is a necessary and sufficient conditions, and second, there are two divisible 25 5, 3 5 125 divisible

172. After zero factorial