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# Find the sum of the first N Dodecagonal Numbers

• Last Updated : 17 Mar, 2021

Given a number N the task is to find the sum of first N Dodecagonal Number.

The first few dodecagonal numbers are 1, 12, 33, 64, 105, 156, 217 …

Examples:

Input: N = 3
Output: 46
Explanation:
1, 12 and 33 are the first three Dodecagonal numbers
Input: N = 5
Output: 215

Approach:

1. Initially, we need to create a function which will help us to calculate the Nth Dodecagonal number.
2. Run a loop starting from 1 to N, to find ith Dodecagonal number.
3. Add all the above calculated Dodecagonal numbers.
4. Finally, display the sum of the first N Dodecagonal numbers.

Below is the implementation of the above approach:

## C++

 `// C++ program to find the sum of``// the first N dodecagonal numbers``#include ``using` `namespace` `std;` `// Function to find the N-th``// dodecagonal number``int` `Dodecagonal_num(``int` `n)``{` `    ``// Formula to calculate N-th``    ``// dodecagonal number``    ``return` `(5 * n * n - 4 * n);``}` `// Function to find the sum of``// the first N dodecagonal numbers``int` `sum_Dodecagonal_num(``int` `n)``{` `    ``// Variable to get the sum``    ``int` `summ = 0;` `    ``// Iterating through the``    ``// first N numbers``    ``for``(``int` `i = 1; i < n + 1; i++)``    ``{``        ` `        ``// Compute the sum``        ``summ += Dodecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver Code``int` `main()``{``    ``int` `n = 5;` `    ``// Display first Nth``    ``// centered_decagonal number``    ``cout << (sum_Dodecagonal_num(n));``    ``return` `0;``}` `// This code is contributed by PrinciRaj1992`

## Java

 `// Java program to find the sum of``// the first N dodecagonal numbers``class` `GFG {``    ` `// Function to find the N-th``// dodecagonal number``static` `int` `Dodecagonal_num(``int` `n)``{` `    ``// Formula to calculate N-th``    ``// dodecagonal number``    ``return` `(``5` `* n * n - ``4` `* n);``}` `// Function to find the sum of``// the first N dodecagonal numbers``static` `int` `sum_Dodecagonal_num(``int` `n)``{` `    ``// Variable to get the sum``    ``int` `summ = ``0``;` `    ``// Iterating through the``    ``// first N numbers``    ``for``(``int` `i = ``1``; i < n + ``1``; i++)``    ``{``       ` `       ``// Compute the sum``       ``summ += Dodecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``int` `n = ``5``;` `    ``// Display first Nth``    ``// centered_decagonal number``    ``System.out.println(sum_Dodecagonal_num(n));``}``}` `// This code is contributed by sapnasingh4991`

## Python3

 `# Python3 program to find the``# sum of the first N``# Dodecagonal numbers` `# Function to find the N-th``# Dodecagonal number``def` `Dodecagonal_num(n):` `    ``# Formula to calculate ``    ``# N-th Dodecagonal``    ``# number ``    ``return` `(``5` `*` `n ``*` `n ``-` `4` `*` `n)``    ` `  ` `# Function to find the``# sum of the first N``# Dodecagonal numbers``def` `sum_Dodecagonal_num(n) :``    ` `    ``# Variable to get the sum``    ``summ ``=` `0``    ` `    ``# Iterating through the``    ``# first N numbers``    ``for` `i ``in` `range``(``1``, n ``+` `1``):` `        ``# Compute the sum``        ``summ ``+``=` `Dodecagonal_num(i)``    ` `    ``return` `summ``  ` `# Driver Code``if` `__name__ ``=``=` `'__main__'` `:``          ` `    ``n ``=` `5``    ` `    ``print``(sum_Dodecagonal_num(n))`

## C#

 `// C# program to find the sum of``// the first N dodecagonal numbers``using` `System;` `class` `GFG {``    ` `// Function to find the N-th``// dodecagonal number``static` `int` `Dodecagonal_num(``int` `n)``{` `    ``// Formula to calculate N-th``    ``// dodecagonal number``    ``return` `(5 * n * n - 4 * n);``}` `// Function to find the sum of``// the first N dodecagonal numbers``static` `int` `sum_Dodecagonal_num(``int` `n)``{` `    ``// Variable to get the sum``    ``int` `summ = 0;` `    ``// Iterating through the``    ``// first N numbers``    ``for``(``int` `i = 1; i < n + 1; i++)``    ``{``        ` `        ``// Compute the sum``        ``summ += Dodecagonal_num(i);``    ``}``    ``return` `summ;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``int` `n = 5;` `    ``// Display first Nth``    ``// centered_decagonal number``    ``Console.WriteLine(sum_Dodecagonal_num(n));``}``}` `// This code is contributed by sapnasingh4991`

## Javascript

 ``
Output:
`215`

Time Complexity: O(N).

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