# Find the sum of the first N Dodecagonal Numbers

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 = 3Output:46Explanation:

1, 12 and 33 are the first three Dodecagonal numbersInput:N = 5Output:215

**Approach:**

- Initially, we need to create a function which will help us to calculate the N
^{th}Dodecagonal number. - Run a loop starting from 1 to N, to find ith Dodecagonal number.
- Add all the above calculated Dodecagonal numbers.
- 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 <bits/stdc++.h>` `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

`<script>` ` ` `// Javascript program to find the sum of` ` ` `// the first N dodecagonal numbers` ` ` ` ` `// Function to find the N-th` ` ` `// dodecagonal number` ` ` `function` `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` ` ` `function` `sum_Dodecagonal_num(n)` ` ` `{` ` ` `// Variable to get the sum` ` ` `let summ = 0;` ` ` `// Iterating through the` ` ` `// first N numbers` ` ` `for` `(let i = 1; i < n + 1; i++)` ` ` `{` ` ` `// Compute the sum` ` ` `summ += Dodecagonal_num(i);` ` ` `}` ` ` `return` `summ;` ` ` `}` ` ` ` ` `let n = 5;` ` ` ` ` `// Display first Nth` ` ` `// centered_decagonal number` ` ` `document.write(sum_Dodecagonal_num(n));` `</script>` |

**Output:**

215

**Time Complexity:** O(N).

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