Lowest prime palindrome greater than time

import java.util.Date;

public class PrimePalindrome{
    protected static long reverseDigits(long num)
    {
        long rev_num = 0;
        while(num > 0)
        {
            rev_num = (rev_num * 10) + (num % 10);
            num = (long)(num * 0.1);
        }
        return rev_num;
    }

    protected static long nextPalindrome(long n) {
        n++;
        long digits = 0;
        long num = n;
        do {
            digits++;
            num = (long)(num * 0.1);
        } while(num > 0);

        long half = (long)(digits * 0.5);
        long left = (long)(n * Math.pow(0.1, half));
        long r_left = reverseDigits(left);
        if(r_left % 2 == 0) {
            long nn1 = (long)(n * Math.pow(0.1, digits-1)) + 1;
            long nn2 = (long)Math.pow(10, digits-1);
            return nextPalindrome(nn1 * nn2);
        }
        long p10h  = (long)Math.pow(10, half);
        long right = n - (left * p10h);

        if(digits % 10 != 0) {
            r_left = reverseDigits((long)(left * 0.1));

            if(r_left > right)
                return (long)(left * p10h) + r_left;
            else {
                ++left;
                return (long)(left * p10h) + reverseDigits((long)(left * 0.1));
            }
        } else {
            if(r_left > right)
                return (long)(left * p10h) + r_left;
            else {
                ++left;
                return (long)(left * p10h) + reverseDigits(left);
            }
        }
    }

    protected static boolean isPrime(long n) {
        if(n == 2)
            return true;
        else if (n == 3)
            return true;
        else if (n % 2 == 0)
            return false;
        else if (n % 3 == 0)
            return false;

        long i = 5;
        long c = 2;
        while(i * i < n) {
            if(n % i == 0)
                return false;
            i += c;
            c = 6 - c;
        }

        return true;
    }

     public static void main(String []args){
        long t = (long)(System.currentTimeMillis() * 0.001);
        System.out.printf("next prime palindrome of %d is ", t);

        long s = System.currentTimeMillis();

        do {
            t = nextPalindrome(t);
        } while(!isPrime(t));

        System.out.println(t);
        System.out.printf("elapsed %d milliseconds", System.currentTimeMillis() - s);
     }
}