1024! How many zeros are there at the end?

The factorial generates 0 because the number contains two or five factors. Obviously, the number of two factors must be greater than the number of five factors. Therefore, you only need to count the number of five factors.

There are several numbers that can be divisible by N from 1 to n: each time one is added to N after five, there can be a number divided by five, therefore, 1024 of the data that can be divisible by 5 is: 1024/5 = 2041024/25 = 40 // those that can be divisible by 25 contain two 5 factors, so 1024/125 = 81024/625 = 1 1 + 8 + 40 + 204 = 253