N-th term in the series 1, 11, 55, 239, 991,...in C++

The given series is 1, 11, 55, 239, 991...

If you clearly observe the series, you will find that the n-th number is 4ⁿ-2^n-1.

Algorithm

• Initialise the number N.
• Use the series formula to compute the n-th term.
• Print the result.

Implementation

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

#include <bits/stdc++.h>
using namespace std;
int getNthTerm(int n) {
   int num = pow(4, n) - pow(2, n) - 1;
   return num;
}
int main() {
   int n = 7;
   cout << getNthTerm(n) << endl;
   return 0;
}

Output

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

16255