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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