Day 25 : Python Program to find the prime factor of a number

 

def prime_factors(n):

    factors = []

    while n % 2 == 0:

        factors.append(2)

        n //= 2

    i = 3

    while i <= n:

        if n % i == 0:

            factors.append(i)

            n //= i

        else:

            i += 2  

    return factors

num = int(input("Enter a number: "))

factors = prime_factors(num)

print(f"Prime factors of {num} are: {factors}")

Code Explanation:

1. Function Definition

def prime_factors(n):

    factors = []

A function named prime_factors is defined to calculate the prime factors of a number n.

An empty list factors is initialized to store the prime factors.

2. Handle Factor of 2 (Even Prime)

while n % 2 == 0:

    factors.append(2)

    n //= 2

This loop continuously divides n by 2 as long as it is divisible by 2.

Each time n is divisible by 2:

2 is added to the factors list.

n is updated to n // 2 (integer division).

After this step, n becomes an odd number because all factors of 2 are removed.

3. Handle Odd Factors

i = 3

while i <= n:

A variable i is initialized to 3 to check for odd factors.

The loop runs as long as i is less than or equal to n.

if n % i == 0:

    factors.append(i)

    n //= i

Inside the loop:

If n is divisible by i, it adds i to the factors list and updates n to n // i.

This process removes all occurrences of the factor i.

else:

    i += 2

If n is not divisible by i, the next odd number (i + 2) is tested as a potential factor.

Only odd numbers are checked because all even factors are already removed.

4. Return the Factors

return factors

Once all factors are processed (i.e., n becomes 1), the function returns the list of prime factors.

5. User Input and Function Call

num = int(input("Enter a number: "))

The user is prompted to input an integer (num) for which the prime factors will be calculated.

factors = prime_factors(num)

print(f"Prime factors of {num} are: {factors}")

The prime_factors function is called with num as its argument.

The returned list of factors is stored in the variable factors and printed to the user.

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