(Palindromic prime) A palindromic prime is a prime number and also palindromic.  For example, 131 is a prime and also a palindromic prime, as are 313 and 757.  Write a program that displays the first 100 palindromic prime numbers.  Display 10 numbers per line, separated by exactly one space, as follows:

2 3 5 7 11 101 131 151 181 191
313 353 373 727 757 787 797 919 929
…

PalindromicPrime.java

/**
 * Palindromic prime number. 
 */

public class PalindromicPrime {

    //** main method */
    public static void main(String[] args) {

		// Declare and initialize variables
		int count=1,number=2;
		String result="";

		while(count<=100){
			if(Prime(number) && Palindromic(number)){ // is the number palindromic prime? 

				if(count%10==0){		
					result += " "+number+"\n";	
				}else{
					result += " "+number;
				}
				count++;		
			}
			number++;

		}

		System.out.print(result); // Print the first palindromic prime numbers.

    } // End of main method.

    /** Prime method */
    public static boolean Prime(int num){

    	// Prime calculation of the first way. This way faster than other ways.
    	int count = 0;
			for(int divisor=2;divisor<=num/2;divisor++){

				if(num%divisor==0){
					return false; // if the number is not prime return false.
				}	
			}	
		return true; // if the number is prime return true.

	/** Prime calculation of the second way.
		int count = 0;
			for(int divisor=2;divisor<=num/2;divisor++){

				if(num%divisor==0){
					count++;
				}	
			}

			if(count==0){
				return true; // if the number is prime return true.
			}
		return false; // if the number is not prime return false.
	*/

	/** Prime calculation of the third way.
		int count = 0;
			for(int divisor=1;divisor<=num/2;divisor++){

				if(num%divisor==0){
					count++;
				}	
			}

			if(count==1){
				return true; // if the number is prime return true.
			}
		return false; // if the number is not prime return false.
	*/

	/** Prime calculation of the fourth way.			
		int count = 0;
			for(int divisor=1;divisor<=num;divisor++){

				if(num%divisor==0){
					count++;
				}	
			}

			if(count==2){
				return true; // if the number is prime return true.
			}
		return false; // if the number is not prime return false.
	*/

	} // End of Prime method.

	/** Palindromic method */
	public static boolean Palindromic(int num){

		// Declare and initialize variables
		int result = 0;
		int number = num;

			// The number reversing.
			while(num!=0){

				int lastDigit= num%10;
				result = result*10+lastDigit;
				num /=10;

			} // End of while num!=0

			if(number==result){
				return true; // if the number is palindromic return true.
			}
		return false; // if the number is not palindromic return false.
	} // End of Palindromic method.	
} // End of class.