HW5.28

 public class Solution
 {
     public static void main(String[] args)
     {
         System.out.printf("%s\t%s\n", "p", "2^p - 1");

         for(int i = 2; i <= 31; i++)
         {
             if(isPrime((int)getMersenne(i)))
                 System.out.printf("%d\t%d\n", i, (int)getMersenne(i));
         }
     }

     public static double getMersenne(int n)
     { return Math.pow(2, n) - 1; }

     public static boolean isPrime(int n)
     {
         if(n == 1)
             return false;
         else if(n == 2)
             return true;
         else
         {
             for(int i = 2; i < n; i++)
             {
                 if(n % i == 0)
                     return false;
             }
             return true;
         }
     }
 }