Sieve of Eratosthenes printable sheet
Printable grids - small 2-100 grids, 2-100 master grid, six-column grid, 2-400 grid
You will need to print one copy of this 2-100 master grid, and a copy of this sheet of smaller grids.
On the first small grid, shade in all the multiples of 2 except 2.
On the second small grid, shade in all the multiples of 3 except 3.
Use the next four small grids to explore what happens for multiples of 4, 5, 6 and 7.
What would change on the master grid if you were to cross out multiples of larger numbers?
We're used to working with grids with ten columns, but you might find an interesting result if you use this six-column grid instead. Can you predict what you will see? Try it!
Imagine you want to find all the prime numbers up to 400.
You could do this by crossing out multiples in a 2-400 number grid.
Which multiples will you choose to cross out?
How can you be sure that you are left with the primes?
(Here is a 2-400 number grid if you want to try it.)
Imagine you want to find all the prime numbers up to 1000 by crossing out multiples in a 2-1000 number grid.
Which number will you cross out last?