public class Emirp{
	
	//trivial prime algorithm, sub in whatever algorithm you want
	public static boolean isPrime(long x){
		if(x < 2) return false;
		if(x == 2) return true;
		if((x & 1) == 0) return false;
		
		for(long i = 3; i <= Math.sqrt(x);i+=2){
			if(x % i == 0) return false;
		}
		
		return true;
	}
	
	public static boolean isEmirp(long x){
		String xString = Long.toString(x);
		if(xString.length() == 1) return false;
		if(xString.matches("[24568].*") || xString.matches(".*[24568]")) return false; //eliminate some easy rejects
		long xR = Long.parseLong(new StringBuilder(xString).reverse().toString());
		if(xR == x) return false;
		return isPrime(x) && isPrime(xR);
	}
	
	public static void main(String[] args){
		int count = 0;
		long x = 1;
		
		System.out.println("First 20 emirps:");
		while(count < 20){
			if(isEmirp(x)){
				count++;
				System.out.print(x + " ");
			}
			x++;
		}
		
		System.out.println("\nEmirps between 7700 and 8000:");
		for(x = 7700; x <= 8000; x++){
			if(isEmirp(x)){
				System.out.print(x +" ");
			}
		}
		
		System.out.println("\n10,000th emirp:");
		for(x = 1, count = 0;count < 10000; x++){
			if(isEmirp(x)){
				count++;
			}
		}
		//--x to fix the last increment from the loop
		System.out.println(--x);
	}
}