# Octahedral Number

Given a number n, the task is to find n-th octahedral number.
A octahedral number belongs to a figurate number and it is the number of spheres in an octahedron built from closely packed spheres. First few octahedral numbers (where n = 0, 1, 2, 3…….) are : 0, 1, 6, 19 and so on.

Examples :

Input : 4
Output : 44

Input : 8
Output : 344

Formula for nth octahedral number:

`n * (2n2+1) / 3`

## C++

 `// C++ program to find nth ` `// octahedral number ` `#include ` `using` `namespace` `std; ` ` `  `// Function to find ` `// octahedral number ` `int` `octahedral_num(``int` `n) ` `{ ` `    ``// Formula to calculate nth ` `    ``// octahedral number ` `    ``return` `n * (2 * n * n + 1) / 3; ` `} ` ` `  `// Drivers code ` `int` `main() ` `{ ` `    ``int` `n = 5; ` ` `  `    ``// print result ` `    ``cout << n << ``"th Octahedral number: "``; ` `    ``cout << octahedral_num(n); ` `    ``return` `0; ` `} `

## Java

 `// Java program to find nth octahedral ` `// number ` `import` `java.io.*; ` ` `  `class` `GFG { ` ` `  `    ``// Function to find octahedral number ` `    ``static` `int` `octahedral_num(``int` `n) ` `    ``{ ` ` `  `        ``// Formula to calculate nth ` `        ``// octahedral number ` `        ``// and return it into main function. ` `        ``return` `n * (``2` `* n * n + ``1``) / ``3``; ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `n = ``5``; ` `        ``// print result ` `        ``System.out.print(n + ``"th Octahedral"` `                         ``+ ``" number: "``); ` `        ``System.out.println(octahedral_num(n)); ` `    ``} ` `} `

## Python3

 `# Python 3 program to find nth ` `# octahedral number ` ` `  `# Function to find ` `# octahedral number ` `def` `octahedral_num(n) : ` `     `  `    ``# Formula to calculate nth ` `    ``# octahedral number ` `    ``return` `n ``*` `(``2` `*` `n ``*` `n ``+` `1``) ``/``/` `3` ` `  `# Driver Code ` `if` `__name__ ``=``=` `'__main__'` `: ` `         `  `    ``n ``=` `5` `    ``print``(n,``"th Octahedral number: "` `                ``, octahedral_num(n)) ` ` `  `# This code is contributed ajit. `

## C#

 `// C# program to find nth  ` `// Octahedral number ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `    ``// Function to find  ` `    ``// octahedral number ` `    ``static` `int` `octahedral_num(``int` `n) ` `    ``{ ` ` `  `        ``// Formula to calculate  ` `        ``// nth octahedral number ` `        ``// and return it into  ` `        ``// main function. ` `        ``return` `n * (2 * n *  ` `                    ``n + 1) / 3; ` `    ``} ` ` `  `    ``// Driver Code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `        ``int` `n = 5; ` `         `  `        ``// print result ` `        ``Console.Write(n + ``"th Octahedral"` `                        ``+ ``" number: "``); ` `        ``Console.WriteLine(octahedral_num(n)); ` `    ``} ` `} ` ` `  `// This code is Contributed by m_kit `

## PHP

 `  `

Output :

```5th Octahedral number: 85
```

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