Prime Numbers and Composite Numbers

1. PRIME NUMBERS AND
COMPOSITE NUMBERS

2. PRIME NUMBERS AND COMPOSITE NUMBERS
Prime
numbers are numbers greater than 1 that only have two factors,
1 and the number itself. This means that a prime number is only
divisible by 1 and itself.

3. PRIME NUMBERS AND COMPOSITE NUMBERS
If you divide a prime number by a number other than 1
and itself, you will get a non-zero remainder.
Example: 13 is a prime number which is divisible by 1 and
itself.

4. Factor is a number which divides a number without any
remainder.
Eg: The factors of 24 are 1, 2,3, 4, 6, 8, 12, 24.
1. If 24 is divided by 5 , it leaves 4 as a remainder.
List the factors of 44
The factors of 44 are 1, 2, 4, 11, 22, 44.

5. PRIME NUMBERS AND COMPOSITE NUMBERS
● Prime numbers are natural numbers greater
than 1.
● 2 is the smallest prime number.
● 2 is the only even prime number. All the prime
numbers except 2 are odd.
● Any two prime numbers are always coprime.

6. PRIME NUMBERS AND COMPOSITE NUMBERS
● Any two prime numbers are always coprime.
● Any composite number can be uniquely expressed as
the product of its prime factors.
● A prime number has only two factors and the number
itself.

7. PRIME NUMBERS AND COMPOSITE NUMBERS
● If two prime numbers have only 1 composite
number between them, they are called twin-
prime numbers.
● Every even positive integer greater than 2 can
be written as the sum of two prime numbers.
● Every positive integer greater than 1 has at
least one prime factor.

8. PRIME NUMBERS AND COMPOSITE NUMBERS
COMPOSITE NUMBER
Composite numbers can be defined as numbers that have
more than two factors.
Eg: 15 is a composite number with factors 1, 3, 5,15.

9. PRIME NUMBERS AND COMPOSITE NUMBERS
■ Factors of 4 = 1, 2, 4 i.e.
Since 4 has more than two factors. So, 4 is a
composite number.
■ Factors of 6 = 1, 2, 3, 6
Since 6 also has more than two factors. So, 6 is also
a composite number.

10. PRIME NUMBERS AND COMPOSITE NUMBERS
SIEVE OF ERATOSTHENES is a method to find prime
numbers and composite numbers. Sieve of Eratosthenes is
a method to find the prime numbers and composite
numbers among a group of numbers. This method was
introduced by Greek Mathematician Eratosthenes in the
third century B.C.

11. PRIME NUMBERS AND COMPOSITE NUMBERS

12. PRIME NUMBERS AND COMPOSITE NUMBERS
Write numbers 2 to 50.
Cross out all multiples of 2 and circle 2.
Cross out all multiples of 3 and circle 3.
Cross out all multiples of 5 and circle 5

13. PRIME NUMBERS AND COMPOSITE NUMBERS
Cross out all multiples of 7 and circle 7
Cross out all multiples of 11 and circle 11.

14. PRIME NUMBERS AND COMPOSITE NUMBERS
So the prime numbers are the unmarked
ones: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37,
41, 43, 47.

15. THANK YOU