Chapter VI Question 27 (Reverse Prime Numbers) (Emirp)

Chapter VI Question 27 (Reverse Prime Numbers) (Emirp)

• **6.27 (Anti-prime number) Anti-prime number (prime number with reverse spelling) refers to a non-palindromic prime number, which is also a prime number after it is reversed. For example: 17 is a prime number, and 31 is also a prime number, so 17 and 71 are inverse prime numbers. Write a program to display the first 100 anti-prime numbers. Each line displays 10, and the numbers are separated by spaces, as shown below:
  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
  …
• Reference Code:

package chapter06;

public class Code_27 {
    
    
    public static void main(String[] args) {
    
    
        int count = 0;
        for (int i = 2;count <= 100;i++){
    
    
            if (isPrime(i) && isPrime(reverse(i)) && !isPalindrome(i)){
    
    
                System.out.print(i + " ");
                count++;
                if (count % 10 == 0)
                    System.out.print("\n");
            }
        }
    }
    public static boolean isPalindrome(int number) {
    
    
        return reverse(number) == number;
    }
    public static int reverse(int number) {
    
    
        int reverseNumber = 0;
        do {
    
    
            reverseNumber = reverseNumber * 10 + number % 10;
            number /= 10;
        }while(number > 0);
        return reverseNumber;
    }
    public static boolean isPrime(int number) {
    
    
        for(int i = 2;i <= Math.sqrt(number);i++)
            if(number % i == 0)
                return false;
        return true;
    }
}

• The results show that:

13 17 31 37 71 73 79 97 107 113 
149 157 167 179 199 311 337 347 359 389 
701 709 733 739 743 751 761 769 907 937 
941 953 967 971 983 991 1009 1021 1031 1033 
1061 1069 1091 1097 1103 1109 1151 1153 1181 1193 
1201 1213 1217 1223 1229 1231 1237 1249 1259 1279 
1283 1301 1321 1381 1399 1409 1429 1439 1453 1471 
1487 1499 1511 1523 1559 1583 1597 1601 1619 1657 
1669 1723 1733 1741 1753 1789 1811 1831 1847 1867 
1879 1901 1913 1933 1949 1979 3011 3019 3023 3049 
3067 
Process finished with exit code 0