**6.27（反素数）反素数（反转拼写的素数）是指一个非回文素数，将其反转之后也是一个素数。例如：17是一个素数，而31也是一个素数，所以17和71是反素数。编写程序，显示前100个反素数。每行显示10个，并且数字间用空格隔开，如下所示：

13 17 31 37 71 73 79 97 107 113

149 157 167 179 199 311 337 347 359 389

**6.27(Emirp)An emirp (prime spelled backward) is a nonpalindromic prime number whose reversal is also a prime. For example, 17 is a prime and 71 is a prime, so 17 and 71 are emirps. Write a program that displays the first 120 emirps. Display 10 numbers per line, separated by exactly one space, as follows:

13 17 31 37 71 73 79 97 107 113

149 157 167 179 199 311 337 347 359 389

``````public class Ans6_27_page202 {
public static void main(String[] args) {
ReverseePrime(100,10);
}
public static void ReverseePrime(int n, int line) {
int count = 0; // Count the number of prime numbers
int number = 2; // A number to be tested for primeness

System.out.println("The first "+n+" numbers are \n");

// Repeatedly find prime numbers
while (count < n) {
String strNumber = number+"";
// Assume the number is prime
boolean isPrime = true; // Is the current number prime?

// Test if number is prime
for (int divisor = 2; divisor <= number / 2; divisor++) {
if (number % divisor == 0) { // If true, number is not prime
isPrime = false; // Set isPrime to false
break; // Exit the for loop
}
}

// Test if number is palindrome
boolean isPalindrome = true;
//String strNumber = number+"";
int low = 0;
int high = strNumber.length() - 1;
while (low < high) {
if (strNumber.charAt(low) != strNumber.charAt(high)) {
isPalindrome = false;
break;
}
low++;
high--;
}

// reverseNumber
int tempNumber = number;
String strReverseNumber = "";
while (tempNumber != 0) {
strReverseNumber += tempNumber % 10;
tempNumber /=10;
}
int reverseNumber = Integer.parseInt(strReverseNumber);
// ReverseePrime
boolean isReverseePrime = true;
for (int divisor = 2; divisor <= reverseNumber / 2; divisor++) {
if (reverseNumber % divisor == 0) {
isReverseePrime = false;
break;
}
}

// Print the prime number and increase the count
if (isPrime && !isPalindrome && isReverseePrime) {
count++; // Increase the count

if (count % line == 0) {
// Print the number and advance to the new line
System.out.println(number);
}
else
System.out.print(number + " ");
}

// Check if the next number is prime
number++;
}
}
}``````