Python program checks prime number

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Example of checking if an integer is a prime number using for loop and if ... else statement. If the number is not a prime number, it will be explained why it is not a prime number in the output.

To understand this example, you should understand the followingPython programmingTopic:

• Python if ... else statement

• Python for Loops

• Python break and continue

greater than1are positive integers, except1and there are no other factors outside, and the number itself is called a prime number.2,3,5,7are prime numbers because they have no other factors.6is not a prime number (it is composite) because2 x 3 = 6.

Source code

# Program checks if a number is a prime number
num =　407
# Get input from the user
#num = int(input("Enter a number: "))
# Prime numbers are greater than1
if num >　1:
　　　# Check character
　　　for i in range(2):
　　　　　　　if (num % i) == 0:
　　　　　　　　　　　print(num, "is not a prime number")
　　　　　　　　　　　print(i, "multiplied by", num//(i, "equals", num)
　　　　　　　　　　　break
　　　else:
　　　　　　　print(num, "is a prime number")
　　　　　　　
# If the input number is less than
# or equal to1It is not a prime number
else:
　　　print(num, "is not a prime number")

Output result

407　is not a prime number
11multiplied by37equals407

In this program, we will check if the variable num is a prime number. Less than or equal to1The number is not a prime number. Therefore, we only check num greater than1to be performed.

We check if num can be2to num-1divisible by any number. If we find a factor in the range, then the number is not a prime number. Otherwise, the number is a prime number.

We can narrow down the range of numbers to find factors.

In the above program, our search range is2to num - 1.

We can use the range[2,num/2]]2,num ** 0.5]. The next range is based on the fact that composite numbers must have factors less than the square root of the number. Otherwise, the number is a prime number.

You can change the value of the variable num in the source code above to check if the number is a prime number of other integers.

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