Check Prime Number in Python

Given a positive integer n, the task is to check whether the number is prime or not in Python. A prime number is a number greater than 1 that has exactly two factors, 1 and itself. For Example:

Input: n = 29
Output: Prime Number

Input: n = 10
Output: Not a Prime Number

Let’s look at the methods below to check for a prime number.

Using flag variable

The program checks whether the number is divisible by any value from 2 to √n. If any divisor is found, the number is not prime; otherwise, it is prime.

True

Explanation:

• n <= 1 checks numbers that are not prime. Loop runs from 2 to √n.
• n % i == 0 checks divisibility and prime becomes False if a divisor is found.

Using isprime() method

This method uses the isprime() function from the SymPy library to check whether a number is prime.

Output

True

Explanation:

• isprime(n) checks whether n is prime.
• Function returns True for prime numbers and False otherwise.

Using Sieve of Eratosthenes

This method creates a list of numbers and marks multiples of each number as non-prime until the target number is reached.

True

Explanation:

• s stores prime status of numbers.
• Multiples of each number are marked False.
• s[n] determines whether the number is prime.

Using Recursion

This approach checks divisibility recursively by reducing the divisor value in each function call.

True

Explanation:

• Function checks whether n is divisible by i. If divisible, it returns False.
• Otherwise, recursion continues with i - 1. If no divisor is found, it returns True.

Related Articles:

• FLAG
• SymPy
• Sieve of Eratosthenes
• Recursion