Next smallest prime palindrome in C++

We are given a number N. We need to find the prime palindrome that is greater than N. Let's see an example.

Input

N = 10

Output

11

Algorithm

• Initialise the number N.

• Write a function to check whether the given number is prime or not.

• Write a function to check whether the given number is palindrome.

• Write a loop that iterates from N + 1 till you find the next prime palindrome.

  • Check if the number is prime and palindrome.
  • If the number is prime and palindrome.
  • Return the number.

Implementation

Following is the implementation of the above algorithm in C++

#include<bits/stdc++.h>
using namespace std;
bool isPrime(int n) {
   if (n < 2) return false;
   for (int i = 2; i <= sqrt(n); i++) {
      if (n % i == 0) return false;
   }
   return true;
}
bool isPalindrome(int n) {
   int num, digit, rev = 0;
   n = num;
   while (num) {
      digit = num % 10;
      rev = (rev * 10) + digit;
      num = num / 10;
   }
return n == rev ? true : false;
}
int getNextSmallestPrimePalindrome(int n) {
   int i = n + 1;
   while (true) {
      if (isPrime(i) && isPalindrome(i)) {
         return i;
      }
      i += 1;
   }
}
int main() {
   int N = 15;
   cout << getNextSmallestPrimePalindrome(N) << endl;
   return 0;
}

Output

If you run the above code, then you will get the following result.

17