Modern C++: Efficient and Scalable Application Development

5. Sexy prime pairs

Sexy prime numbers are prime numbers that differ from each other by six (for example 5 and 11, or 13 and 19). There are also twin primes, which differ by two, and cousin primes, which differ by four.

In the previous challenge, we implemented a function that determines whether an integer is a prime number. We will reuse that function for this exercise. What you have to do is check that if a number n is prime, the number n+6 is also prime, and in this case print the pair to the console:

int main(){   int limit = 0;   std::cout << "Upper limit:";   std::cin >> limit;   for (int n = 2; n <= limit; n++)   {      if (is_prime(n) && is_prime(n+6))      {         std::cout << n << "," << n+6 << std::endl;      }   }}

You could take it as a further exercise to compute ...