Python program to check prime numbers

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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, it explains why it is not a prime in the output.

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

• Python if ... else statement

• Boucles for en Python

• break et continue en Python

greater than1is a positive integer, except1and there are no other factors outside, and the number itself is called a prime.2,3,5,7are prime numbers because they have no other factors.6is not a prime (it is composite), because2 x 3 = 6.

Source code

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

Output results

407　is not a prime
11multiplied by37equals407

In this program, we will check if the variable num is a prime. Less than or equal to1The number is not a prime.1is performed.

We check if num can be divided by2to num-1divisible by any number. If we find a factor within this range, then the number is not a prime. Otherwise, the number is a prime.

We can narrow 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], or [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.

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

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