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Program to check if the given number is Prime or not in Python

Program to check if the given number is Prime or not in Python

Prime number or not

A number is said to be a prime number if and only if it is only divisible by 1 or itself (factors==>1,number itself) . If a number has more than two factors than the number is said to be not a prime number.

  • Sample input: 17
  • Sample output: The given number is prime

See the two different approaches below , solution 1 is more efficient than solution 2

Working:

  • Step 1: Intialize the variable a and count to zero
  • Step 2: Read the input
  • Step 3: Set a to n//2 (// in python implies integer division) , we can make a to square root of number to make it more efficient
  • Step 4: iterate through 2 to a+1 and check whether it is divisible by i or not
  • Step 5 : if divisible , then print “not a prime number” and set count to 1 and break from the loop
                  else continue iteration
  • Step 6 : if count is still zero then the given number is prime number

Python code:

Solution 1:

a = 0
count = 0
n=int(input(“Enter the number to check if it is prime or not: “))
a = n // 2;
for i in range(2,a+1):
    if (n % i == 0):
        print(“The given number is not prime”)
        count = 1
        break
if (count == 0):
    print(“The given number is prime”)
Enter the number to check if it is prime or not: 17
The given number is prime

Working:

  • Step 1: Take an empty array
  • Step 2: Read the number
  • Step 3: iterate a for loop from 1 to the number
  • Step 4: If number is divisible by iterator i then append the number to factors array
  • Step 5: if length of factors array is 2 then given number is prime
                 else the given number is not prime number
    (for more clarity factors of numbers also printed)

Solution 2:

factors=[ ]
n=int(input(“Enter the number to check if it is prime or not: “))
for i in range(1,n+1):
    if (n % i == 0):
        factors.append(i)
if (len(factors)==2):
    print(“The given number is prime”)
else:
    print(“The given number is not prime number”)
print(“Factors of given number is”,factors)
Enter the number to check if it is prime or not: 16
The given number is not prime number
[1, 2, 4, 8, 16]