###
**Given the following function and it's results:**

###
**f(x,y) = x^y + y^x where x>0 and y>1****f(1,2) = 1^2 + 2^1 = 3****f(2,3) = 2^3 + 3^2 = 17****f(3,4) = 3^4 + 4^3 = 145****.**** .**** .**

###
**Using the above function denoted by f(x,y), and given that the initial values of x = 1 and y = 2, which increase by 1 each time, what are the last 4 digits of the sum of the first 15 function calls.**

**Language C++:**

```
#include<iostream>
using namespace std;
class power_fun {
private:
long long int sum,last_4_digit;
public:
power_fun () {
sum = 0;
last_4_digit = 0;
}
void show_last_digit() {
int x = 1,y = 2,i;
for(i = 0 ; i < 15 ; i++) {
sum = sum + function_solver(x,y);
x++;
y++;
}
cout<<"sum = "<<sum<<endl;
last_4_digit = sum % 10000;
cout<<"last_4_digit = "<<last_4_digit<<endl;
}
long long int function_solver(int xx,int yy) {
long long int t1 = 1,t2 = 1;
int i;
for (i = 1 ; i <= yy ; i++)
t1 = t1*xx;
for (i = 1 ; i <= xx ; i++)
t2 = t2*yy;
return(t1+t2);
}
};
int main() {
power_fun obj;
obj.show_last_digit();
return(0);
}
```