CodePudding user response:

Prime Numbers is also called the prime, a natural number greater than 1, besides 1 and itself, cannot be divided exactly by other natural number is called the prime
In python ceil () function is to return a digital into an integer,
If a number is not a prime number, such as 12, 1,2,3,4,6,12 his factor, we found that the factor is the square root of 12 is divided into two parts but the product of the corresponding to the two parts are the 12,, so only half validation shows that he is not a prime number
Range (left) do not take right so
Assuming that number is 9, the factor 1,3,9. At this time his square is 3, so if we don't look at 9 can be divided exactly by 3 then 9 to prime the not right
So the value add 1

# # I understand so are for reference only