Prime and Composite Numbers
Let’s observe the factors of few natural numbers.
We can see that number 1 has only one factor (i.e.
itself).There are numbers that have exactly two factors i.e.1 and the number
itself. Such numbers are 2, 3, 5, etc. These numbers are prime numbers.
number is called prime when it can't be divided evenly by any number except 1
Therefore, Prime numbers are natural
numbers that have only 2 factors i.e. 1 and itself.
19 have only two factors, 1 and 19. 19 cannot be
divided evenly by numbers other than 1 or itself. So, 19 is a prime number.
Co – Prime Numbers
The two numbers are said to be co-prime
numbers when there is no number, other than 1, that divides both the two given
number evenly. The HCF of these numbers should be 1.
Example: 6 and 35 are co-prime
Let’s observe factors of natural numbers again.
There are numbers having more than two factors like 4,
6, etc. These numbers are composite numbers. When a number can
be divided up evenly it is a Composite Number. A composite number
has factors in addition to one and itself.
Therefore, numbers having more than two
factors are called Composite numbers.
15 have three factors, 1, 5 and 15. 15 can be divided
evenly by numbers other than 1 or itself. So, 15 is a composite number.
Prime and Composite Number Chart (1 to 100)
1. 1 is neither a prime nor a composite number.
2. All the numbers in orange box are prime numbers. All
the numbers in white box, other than 1 are composite numbers.
1. The numbers 0 and 1 are neither prime nor composite.
2. Every prime number except 2 is odd.
3. HCF of two prime numbers is always 1
4. Even numbers are divisible by two and so all even
numbers greater than two are composite numbers. Example: 2, 4, 6, 8, 10
5. 1 is co-prime with every number.
6. Every prime number is co-prime to each other. Example:
3 and 5
7. Any two successive numbers are always co-primes.
8. The sum two prime numbers can be even or odd.