All composite numbers can be expressed as unique products of prime numbers. This is accomplished by dividing the original number and its factors by prime numbers until all the factors are prime. A factor tree can help you visualize this.
Example: 210
210 Divide by two.
105,2 Divide by three.
35,3,2 Divide by five.
7,5,3,2 Stop. All the factors are prime.
2 x 3 x 5 x 7 = 210
That's the prime factorization of 210.
A factor tree
999 333,1 111,3,3 37,3,3,3
3, 3, 3 and 3
1997 is already prime; no tree.
63 / × \ 7 × 9 / /\ 7 × 3×3
96 48,2 24,2,2 12,2,2,2 6,2,2,2,2 3,2,2,2,2,2
a prime factorization tree
33 11,3
51 3,17
350=2x5x5x7
by using a prime factor tree
3 is already prime; no tree.