Below is a factor tree.  You should know some of the smaller prime
numbers: 2,3,5,7,11,13,17,19,23,29,31,37,41


                 702
                 / \
               351× 2 <-(prime)
                /\
             117× 3 <-(prime)
              /\
            39× 3 <-(prime)
            /\
(prime)-> 13× 3 <-(prime) 

I wrote 702 on the top line. Then I found the smallest prime that 
would divide evenly into 702.  That was 2, So I broke 702 down to 
351×2 on the second line. Then I found the smallest prime that 
would divide evenly into 351. That was 3, So I broke 351 down to 
117×3 on the third line. Then I found the smallest prime that would 
divide evenly into 117. That was 3, So I broke 117 down to 39×3 on 
the fourth line.  Then I found the smallest prime that would divide 
evenly into 39. That was 3, So I broke 39 down to 13×3 on the fifth 
line. Then I discovered that 13 was also prime, and so I knew that I
was done with the tree.

So I put down the product of all the primes from the top down and
got:

    702 = 2×3×3×3×13

and since 3 appears 3 times I write it simpler using an exponent of 3:

    702 = 2×3³×13

Edwin