Prime Number



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Checking if a Number is Prime

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. In other words, a prime number has exactly two distinct factors: 1 and the number itself.

To determine whether a number is prime, we can use a method that involves checking divisibility by numbers starting from 2 up to the square root of the given number. If the number is divisible by any of these, it is not prime. If no divisors are found, the number is prime.

Examples

Let’s examine some examples to see how this method works in practice.

1. Check if 13 is a prime number.

Answer

First, we identify the given number:

Given:

  • n = 13

Next, we calculate the square root of 13, which is approximately 3.6. We then check if 13 is divisible by any number from 2 up to 3 (the integer part of the square root):

Steps:

  • Check divisibility by 2: 13 % 2 ≠ 0
  • Check divisibility by 3: 13 % 3 ≠ 0

Since 13 is not divisible by any of these numbers, it has no divisors other than 1 and 13 itself.

Result:

∴ 13 is a prime number.

2. Check if 10 is a prime number.

Answer

We start by identifying the number:

Given:

  • n = 10

The square root of 10 is approximately 3.2. We check if 10 is divisible by any number from 2 up to 3:

Steps:

  • Check divisibility by 2: 10 % 2 = 0

Since 10 is divisible by 2, it has a divisor other than 1 and itself.

Result:

∴ 10 is not a prime number.

3. Determine if 17 is a prime number.

Answer

We begin by identifying the number:

Given:

  • n = 17

The square root of 17 is approximately 4.1. We check if 17 is divisible by any number from 2 up to 4:

Steps:

  • Check divisibility by 2: 17 % 2 ≠ 0
  • Check divisibility by 3: 17 % 3 ≠ 0
  • Check divisibility by 4: 17 % 4 ≠ 0

Since 17 is not divisible by any of these numbers, it has no divisors other than 1 and 17 itself.

Result:

∴ 17 is a prime number.

4. Verify if 25 is a prime number.

Answer

We start by identifying the number:

Given:

  • n = 25

The square root of 25 is exactly 5. We check if 25 is divisible by any number from 2 up to 5:

Steps:

  • Check divisibility by 2: 25 % 2 ≠ 0
  • Check divisibility by 3: 25 % 3 ≠ 0
  • Check divisibility by 4: 25 % 4 ≠ 0
  • Check divisibility by 5: 25 % 5 = 0

Since 25 is divisible by 5, it has a divisor other than 1 and itself.

Result:

∴ 25 is not a prime number.

Frequently Asked Questions (FAQs)

1. What is a prime number?

2. How does the check prime number tool work?

3. Can negative numbers be prime numbers?

4. Is the number 1 a prime number?

5. How can I use the tool to check if a number is prime?

6. Why is the number 2 considered a prime number?

7. Can large numbers be prime?

8. What are some common examples of prime numbers?