What is Prime Number?

 

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself.

Prime numbers are numbers that have only 2 factors: 1 and themselves. For example, the first 5 prime numbers are 2, 3, 5, 7, and 11. By contrast, numbers with more than 2 factors are call composite numbers.

 1 to 100 all Prime Numbers list

When a number has more than two factors it is called a composite number. Here are the first few prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, etc.

Prime number is a number that is greater than 1 and divided by 1 or itself only. In other words, prime numbers can't be divided by other numbers than itself or 1. For example 2, 3, 5, 7, 11, 13, 17.... are the prime numbers.

Program for Prime Number: 

 import java.util.Scanner;    

2.    import java.util.Scanner;  

3.    public class PrimeExample3

4.     {  

5.       public static void main(String[] args)

6.     {  

7.           Scanner s = new Scanner(System.in);  

8.           System.out.print("Enter a number : ");  

9.           int n = s.nextInt();  

10.        if (isPrime(p))

11.           {  

12.            System.out.println(p + " is a prime number");  

13.            } 

14.               else 

15.           {  

16.            System.out.println(p + " is not a prime number");  

17.        }  

18.    }  

19.   

20.    public static boolean isPrime(int p) 

21.       {  

22.        if (p <= 1) 

23.          {  

24.            return false;  

25.          }  

26.        for (int i = 2; i < Math.sqrt(p); i++)

27.            {  

28.            if (p % i == 0) 

29.              {  

30.                return false;  

31.              }  

32.        }  

33.        return true;  

34.    }  

35. }