Answer to Question 17A-2

// numPrimes(n) returns the number of values in
// list [1,...,n] that are prime.

int numPrimes(const int n)
{
  if(n < 2)
  {
    return 0;
  }
  else 
  {
    int m = numPrimes(n-1);
    if(isPrime(n))
    {
      return m;
    }
    else
    {
      return m + 1;
    }
  }
}