Sieve of Eratosthenes, 400 numbers

This printable sieve of Eratosthenes is 400 numbers long (instead of the usual 100). 

The Sieve of Eratosthenes is a good way to find small prime numbers. It goes as follows:

1. Cross out number 1

2. Circle next number that is not crossed out (the first one is 2)

3. Cross out numbers that are divisible by number you just circled

Repeat faces 2 and 3 until there are nothing but primes left.

This longer version gives interested students a possibility to examine further, how much prime numbers there are when we go further with the natural numbers. (This is interesting, because it kind of connects very simple school math with higher level mathematics. If students want to examine further, for example from Wikipedia, they will realize that the density of prime numbers (prime number theorem) is something that a number of very skilled mathematicians have spent countless hours with. 

Of course, knowing the first prime number is essential to survive with more complicated fractions in secondary mathematics (or higher). That way, faster students can find all the primes lower than 400 in the same time when some students may be able to find only the smaller ones. Each of these student groups will at the end of the day benefit from it. 

This one is free! The pdf is not editable and most suitable for printing and then doing with pencil and paper. This goes with different grade levels from upper elementary to high school. 

2 pages pdf, one instruction & task page, one answer page.