Check if Number is Prime in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of prime check for number 29

What is the output of this code when checking if 29 is prime?

DSA Python

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

print(is_prime(29))

A True

B False

C None

D Error

💡 Hint

Check divisors from 2 up to square root of the number.

29 is a prime number because it has no divisors other than 1 and itself.

❓ Predict Output

intermediate

Output of prime check for number 1

What is the output of this code when checking if 1 is prime?

DSA Python

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

print(is_prime(1))

A True

B False

C None

D Error

💡 Hint

Numbers less than or equal to 1 are not prime.

1 is not a prime number by definition.

🔧 Debug

advanced

Identify the error in prime check code

What error does this code produce when checking if 10 is prime?

DSA Python

def is_prime(n):
    if n <= 1
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

print(is_prime(10))

A No error, outputs False

B TypeError

C NameError

D SyntaxError

💡 Hint

Check the line with the if statement for missing punctuation.

The if statement is missing a colon, causing a SyntaxError.

❓ Predict Output

advanced

Output of prime check for number 25

What is the output of this code when checking if 25 is prime?

DSA Python

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

print(is_prime(25))

A False

B True

C None

D Error

💡 Hint

Check if 25 has divisors other than 1 and itself.

25 is divisible by 5, so it is not prime.

🧠 Conceptual

expert

Why check divisors only up to square root?

Why does the prime check function only test divisors up to the square root of the number?

A Because the square root is the largest possible divisor

B Because numbers larger than the square root are always prime

C Because any factor larger than the square root pairs with a smaller factor already checked

D Because checking beyond the square root causes runtime errors

💡 Hint

Think about factor pairs and multiplication.

If a number has a factor larger than its square root, it must pair with a smaller factor already checked.