Prime Numbers
- The numbers whose only factors are 1 and the number itself are called the Prime Numbers.
- Example : 2, 3, 5, 7, 11 etc.
Composite Numbers
- All the numbers with more than 2 factors are called composite numbers or you can say that the numbers which are not prime numbers are called Composite Numbers.
- Example - 4, 6, 8, 10, 12 etc.
Remark: 1 is neither a prime nor a composite number.
Sieve of Eratosthenes Method
This is the method to find all the prime numbers from 1 to 100.
Step 1: First of all cross 1, as it is neither prime nor composite.
Step 2: Now mark 2 and cross all the multiples of 2 except 2.
Step 3: Mark 3 and cross all the multiples of 3 except 3.
Step 4: 4 is already crossed so mark 5 and cross all the multiples of 5 except 5.
Step 5: Continue this process until all the numbers are marked square or crossed.
This shows that all the covered numbers are prime numbers and all the crossed numbers are composite numbers except 1.