1. +
Factors of natural numbers
2010-Baghdad

2. +
Factor:
 A factor of a natural number n is any number that divides nwith
zero remainder.
 For example, the factors (divisors) of 20 are 1, 2, 4, 5, 10, and
20. The factors of 25 are 1, 5, and 25. The factors of 37 are 1
and 37.

3. +
Prime Numbers
 A prime number is a natural number that has only two factors, 1
and the number itself.

4. +
Composite Numbers
 Natural numbers which have more than two factors are called
composite numbers.

5. +
Prime numbers less than 100

6. +
Prime factorization of natural
numbers
 The prime factors of a number are the factors of the number
which are prime.
 Example: The factors of 30 are {1, 2, 3, 5, 6, 10, 15, 30}.
Therefore, 2, 3, and 5 are the prime factors of 30.

7. +
Prime Factorization
 Writing a natural number as a product of its prime factors is
called the prime factorization of the natural number.
 To find prime factors of a natural number, we divide the number
by the smallest possible prime factor each time, and stop when
the quotient reaches 1.

8. +
Example:
Lets find prime factors of 180.
180 2 180 ÷ 2 = 90 (divide 180 by 2, quotient is 90)
90 2 90 ÷ 2 = 45(divide 90 by 2, quotient is 45)
45 3 45 ÷ 3 = 15 (divide 45 by 3, quotient is 15)
15 3 15 ÷ 3 = 5 (divide 15 by 3, quotient is 5)
5 5 5 ÷ 5 = 5 (divide 5 by 5, quotient is 1)
1 stop
180 = 2.2.3.3.5