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# Find the sum of the first Nth Heptadecagonal Number

• Last Updated : 18 Mar, 2021

Given a number N, the task is to find the sum of first N Heptadecagonal Numbers.

The first few heptadecagonal numbers are 1, 17, 48, 94, 155, 231 …

Examples:

Input: N = 3
Output: 66
Explanation:
1, 17 and 48 are the first three heptadecagonal numbers.
Input: N = 6
Output: 546

Approach:

1. Initially, we need to create a function which will help us to calculate the Nth heptadecagonal number.
2. Now, run a loop starting from 1 to N, to find ith heptadecagonal number.
4. Finally, display the sum of the first N heptadecagonal numbers.

Below is the implementation of the above approach:

## C++

 `// C++ program to find the sum of the``// first N heptadecagonal numbers``#include ``using` `namespace` `std;` `// Function to find the N-th``// heptadecagonal number``int` `heptadecagonal_num(``int` `n)``{``    ` `    ``// Formula to calculate nth``    ``// heptadecagonal number``    ``return` `((15 * n * n) - 13 * n) / 2;``}` `// Function to find the sum of the``// first N heptadecagonal numbers``int` `sum_heptadecagonal_num(``int` `n)``{``    ` `    ``// Variable to store the sum``    ``int` `summ = 0;``    ` `    ``// Iterating from 1 to N``    ``for``(``int` `i = 1; i < n + 1; i++)``    ``{``       ` `       ``// Finding the sum``       ``summ += heptadecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver code``int` `main()``{``    ``int` `n = 5;``    ` `    ``cout << sum_heptadecagonal_num(n);``}` `// This code is contributed by coder001`

## Java

 `// Java program to find the sum of the``// first N heptadecagonal numbers``class` `GFG{``    ` `// Function to find the N-th``// heptadecagonal number``public` `static` `int` `heptadecagonal_num(``int` `n)``{``        ` `    ``// Formula to calculate nth``    ``// heptadecagonal number``    ``return` `((``15` `* n * n) - ``13` `* n) / ``2``;``}``    ` `// Function to find the sum of the``// first N heptadecagonal numbers``public` `static` `int` `sum_heptadecagonal_num(``int` `n)``{``        ` `    ``// Variable to store the sum``    ``int` `summ = ``0``;``        ` `    ``// Iterating from 1 to N``    ``for``(``int` `i = ``1``; i < n + ``1``; i++)``    ``{``        ` `       ``// Finding the sum``       ``summ += heptadecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver code    ``public` `static` `void` `main(String[] args)``{``    ``int` `n = ``5``;``    ` `    ``System.out.println(sum_heptadecagonal_num(n));``}``}` `// This code is contributed by divyeshrabadiya07`

## Python3

 `# Python3 program to find the sum``# of the first N ``# heptadecagonal numbers` `# Function to find the``# N-th heptadecagonal``# number``def` `heptadecagonal_num(n):` `    ``# Formula to calculate ``    ``# nth heptadecagonal``    ``# number``    ``return` `((``15` `*` `n ``*` `n) ``-` `13` `*` `n) ``/``/` `2``    ` `  ` `# Function to find the``# sum of the first N``# heptadecagonal numbers``def` `sum_heptadecagonal_num(n) :``    ` `    ``# Variable to store``    ``# the sum``    ``summ ``=` `0``    ` `    ``# Iterate from 1 to N``    ``for` `i ``in` `range``(``1``, n ``+` `1``):` `        ``summ ``+``=` `heptadecagonal_num(i)``    ` `    ``return` `summ``  ` `# Driver code``if` `__name__ ``=``=` `'__main__'` `:``          ` `    ``n ``=` `5``    ` `    ``print``(sum_heptadecagonal_num(n))`

## C#

 `// C# program to find the sum of the``// first N heptadecagonal numbers``using` `System;` `class` `GFG{``    ` `// Function to find the N-th``// heptadecagonal number``public` `static` `int` `heptadecagonal_num(``int` `n)``{``        ` `    ``// Formula to calculate nth``    ``// heptadecagonal number``    ``return` `((15 * n * n) - 13 * n) / 2;``}``    ` `// Function to find the sum of the``// first N heptadecagonal numbers``public` `static` `int` `sum_heptadecagonal_num(``int` `n)``{``        ` `    ``// Variable to store the sum``    ``int` `summ = 0;``        ` `    ``// Iterating from 1 to N``    ``for``(``int` `i = 1; i < n + 1; i++)``    ``{``        ` `       ``// Finding the sum``       ``summ += heptadecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `n = 5;``    ` `    ``Console.WriteLine(sum_heptadecagonal_num(n));``}``}` `// This code is contributed by Code_Mech`

## Javascript

 ``
Output:
`315`

Time complexity: O(N).

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