Prime numbers may seem odd – most are – yet this set of numbers are like building blocks to so many numerical wonders!

I have a favorite activity that I stumbled across years ago. Students tend to enjoy it because it is simple – and relaxing in a way similar to coloring. It is helpful to have paper with large grids – graph paper with squares large enough in which to write numbers.

Students begin by simply writing numbers, one per box and ten per row.

Students highlight “1” and “2” – our unusual pair. Then they mark off (either placing an “x” through the box or filling it in) every second box. Counting by two’s, they fill in all the multiples of two – thus numbers which are not prime, having a factor other than one and itself.

Next, students go back and mark off every third box – filling in all the multiples of three. Again, these are numbers that are not prime (called composite). As they do this, they notice that some – a pattern of every other mark – is already filled in because it was also a multiple of two.

Students want to continue with every fourth number, however, all of these are already marked off! (Being that four is, itself, a multiple of two – which was already completed.) So, they go on to every fifth (the next non-marked number) and notice that there are quite a few already marked off – another pattern here? Yes!

By continuing in this way until they reach the last “unmarked” number in their grids, they are left with composite numbers marked away leaving only prime numbers visible! They have also begun to recognize patterns in numbers and the basics of factors.