Finding Primes Activity (Sieve of Eratosthenes)
There is a way to find prime numbers that was used by the ancient Greeks. See if you can follow the reasoning.
A Visual Method for Finding Prime Numbers
Question 1)
We crossed out the number 1 in Step 1. How do we know that 1 is not a prime number?
Question 2)
In Step 3, we crossed out the multiples of 2 (that were bigger than 2). How do we know these numbers are not prime?
Question 3)
List all of the prime numbers between 1 and 100.
Question 4)
A lot of the numbers ending with the digit 1 are prime. However, 51 is not a prime number. List all the factors of 51 and explain why it is not a prime number.
Question 5)
In our example, we could stop with the multiples of 7. Can you explain why? (Hint: It depends on the size of the grid).