Sk i l l s H a n d b o o k
Pr i m e N u m b er s an d Co m p o si t e N u m b er s
A prim e n u m b e r is a w hole n u m b e r greater th a n 1 th a t h as exactly two factors,
the n u m b e r 1 a n d itself.
Prime num ber 2 5 17 29
Factors 1,2 1,5 1, 17 1,29
A com posite n u m b e r is a n u m b e r th a t h as m ore th a n two factors. The n u m b e r 1 is
neith er prim e n o r com posite.
Composite number 6 1 5 4 8
Factors 1, 2, 3, 6 1, 3, 5, 15 1, 2, 3, 4, 6 , 8 , 12, 16, 24, 48
Ex a m p l e 1
Is 51 prime or com posite?
51 = 3 • 17 Try to find factors other than 1 and 51.
51 is a com posite num ber.
You can use a factor tree to find th e p rim e factors of a num ber. W hen all th e factors
are prim e n um bers, it is called th e p rim e factorization of th e num ber.
Ex a m p l e 2
Use a factor tree to write the prime factorization o f 28.
2 g 28 The order o f listing the factors may be different,
/ \ / \ but the prime factorization is the same.
2 14 4 7
\2 ) [1J [2J (2
The prim e factorization of 28 is 2 • 2 • 7.
Ex e r c i se s
Is each num ber prime or com posite?
1.9 2.16 3.34 4.61 5.7 6.13
7.12 8.40 9.57 10.64 11.120 12.700
List all the factors o f each number.
13.46 14.32 15.11 16.65 17.27 18.29
Use a factor tree to write the prim e factorization o f each number.
- 18 20. 20 21. 27 22. (^5423). 64 24. 96