Prime number is a number where the number can be divided by 1 and/or itself only. Which means the number is not able to be divided by any numbers other than 1 and/or itself.  For example 2, 3, 5, 7, 11, 13, 17.... are the prime numbers.

Note: 0 and 1 are not prime numbers. The 2 is the only even prime number because all the other even numbers can be divided by 2.

Application:
  • Cryptography Example RSA, Deffie Hellman, DSA
  • Hash Codes
  • Highest Common Factor (HCF) and the Lowest Common Multiple (LCM) of two (or more) large numbers
  • Bank Credit Card Security.

Prime Number Program using Method in Java

public class PrimeExample2{  
static void checkPrime(int n){
  int i,m=0,flag=0;    
  m=n/2;    
  if(n==0||n==1){
   System.out.println(n+" is not prime number");    
  }else{
   for(i=2;i<=m;i++){    
    if(n%i==0){    
     System.out.println(n+" is not prime number");    
     flag=1;    
     break;    
    }    
   }    
   if(flag==0)  { System.out.println(n+" is prime number"); }
  }//end of else
}
 public static void main(String args[]){  
  checkPrime(1);
  checkPrime(3);
  checkPrime(17);
  checkPrime(20);
}  
} 



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