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n’th Pentagonal Number in C++
In this tutorial, we are going to write a program that finds the n-th pentagonal number.
A pentagonal number is a number represented as dots or pebbles arranged in the shape of a regular polygon. Refer to the wiki for better understanding.
The n-th pentagonal number is (3 * n * n - n) / 2.
The series of pentagonal numbers are 1, 5, 12, 22, 35, 51, 70, 92...
Algorithm
- Initialise the number n.
- Use the formula to find the n'th pentagonal number.
- Print the resultant number.
Implementation
Following is the implementation of the above algorithm in C++
#include<bits/stdc++.h>
using namespace std;
int getNthPentagonalNumber(int n) {
return (3 * n * n - n) / 2;
}
int main() {
int n = 7;
cout << getNthPentagonalNumber(n) << endl;
return 0;
}Output
If you run the above code, then you will get the following result.
70
Updated on: 22-Oct-2021
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