Problem #44

I had to re do this one three different times because I kept messing it up lol.

#include <iostream>
#include <ctime>
#include <cmath>

using namespace std;
 
unsigned long long int pent(unsigned long long int n);
bool ipent(unsigned long long int n);
 
int main(void) 
{
    clock_t start = clock();
    int total = 0;

    for (unsigned long long int i = 1; i < 3000; i++) 
        for (unsigned long long int j = 1; j < i; j++) 
            if (ipent(pent(i) + pent(j))) 
                if (ipent(pent(i) - pent(j))) 
                    total = pent(i) - pent(j);

    cout << total << endl 
         << "Process took " << (static_cast<double> (clock()) - start) / CLOCKS_PER_SEC << " seconds." << endl;
    system("pause");
    return 0;
}

unsigned long long int pent(unsigned long long int n) 
{
    return n * (3 * n - 1) / 2;
}

bool ipent(unsigned long long int n) 
{
    if (floor((1 + sqrt(static_cast<double> (1 + 24 * n))) / 6) == ceil((1 + sqrt(static_cast<double> (1 + 24 * n))) / 6))
        return true;
    return false;
}