Now, we know that 2 is used up!

Try 3 next:


660 / 2 = 330 / 2 = 165 / 3 = 55  ...  I used the 3 divisibility test to see that 3 goes in!

 

3 is used up...  Go to 5 next:


660 / 2 = 330 / 2 = 165 / 3 = 55 / 5 = 11  ...  When this is prime, STOP!

 

660 / 2 = 330 / 2 = 165 / 3 = 55 / 5 = 11  ...  Now, just go down the stack to get your answer!

 

660 = 2 x 2 x 3 x 5 x 11

660 = 2^2 x 3 x 5 x 11