Prime Numbers
Prime & Composite Numbers
Prime & Composite Numbers
Prime numbers are numbers that have exactly 2 factors: 1 and itself.
Prime numbers are numbers that have exactly 2 factors: 1 and itself.
Composite numbers are numbers that have 3 or more factors.
Composite numbers are numbers that have 3 or more factors.
The only natural number that is neither Prime nor Composite is 1. The number 1 is often referred to as the multiplicative identity or the empty product.
The only natural number that is neither Prime nor Composite is 1. The number 1 is often referred to as the multiplicative identity or the empty product.
Watch this video to learn more about prime numbers!
Watch this video to learn more about prime numbers!
Try it!
Try it!
Use the applet below to run the Sieve of Eratosthenes to identify Prime numbers.
Use the applet below to run the Sieve of Eratosthenes to identify Prime numbers.
Step 1: Look for the smallest unidentified prime number (Eg. 2)
Step 1: Look for the smallest unidentified prime number (Eg. 2)
Step 2: Remove all its multiples (Eg. 4, 6, 8, 10, etc).
Step 2: Remove all its multiples (Eg. 4, 6, 8, 10, etc).
Step 3: The next larger number that has not been removed (Eg. 3) is a prime number.
Step 3: The next larger number that has not been removed (Eg. 3) is a prime number.
Step 4: Go back to Step 3 until you run out of numbers to remove.
Step 4: Go back to Step 3 until you run out of numbers to remove.
Why do you think 1 is not a prime number?
Why do you think 1 is not a prime number?
A simple reason is that if 1 was a prime number then using the Sieve to remove all multiples of 1, the game would be over before it even began.
A simple reason is that if 1 was a prime number then using the Sieve to remove all multiples of 1, the game would be over before it even began.
Link: Let's practice Prime Factorisation!
Link: Let's practice Prime Factorisation!