Given a number **N**, the task is to count the number of triangles required to form a House of Cards of **N** levels.

**Examples:**

Input:N = 3Output:13Explanation:

From the above image, the following observations can be made:

Count of triangles of unit 1 = 9 (6 non-inverted triangles and 3 inverted triangles)

Count of triangles of unit 2 = 3

Count of triangles of unit 3 = 1

Therefore, total number of triangles = 6 + 3 + 3 + 1 = 13

Input:N = 2Output:5

**Approach: **The required number of triangles required to form a House of Cards of **N** levelscan be calculated by the formula:

**Illustration:**

For N = 3

Count of triangles = 3 * (3 + 2) * (6 + 1) / 8 = 13For N = 2

Count of triangles = 2 * (2 + 2) * (4+ 1) / 8 = 5

Below is the implementation of the above approach:

## CPP

`// C++ implementation of the` `// above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the` `// number of triangles` `int` `noOfTriangles(` `int` `n)` `{` ` ` `return` `floor` `(n * (n + 2)` ` ` `* (2 * n + 1) / 8);` `}` `// Driver Code` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `// Function call` ` ` `cout << noOfTriangles(n) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java implementation of the` `// above approach` `import` `java.lang.*;` `class` `GFG {` ` ` `// Function to find number of triangles` ` ` `public` `static` `int` `noOfTriangles(` `int` `n)` ` ` `{` ` ` `return` `(n * (n + ` `2` `) * (` `2` `* n + ` `1` `) / ` `8` `);` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `main(String args[])` ` ` `{` ` ` `int` `n = ` `3` `;` ` ` `// Function call` ` ` `System.out.print(noOfTriangles(n));` ` ` `}` `}` |

## Python3

`# Python3 implementation of` `# the above approach` `# Function to find required` `# number of triangles` `def` `noOfTriangles(n):` ` ` `return` `n ` `*` `(n ` `+` `2` `) ` `*` `(` `2` `*` `n ` `+` `1` `) ` `/` `/` `8` `# Driver Code` `n ` `=` `3` `# Function call` `print` `(noOfTriangles(n))` |

## C#

`// C# implementation of the` `// above approach` `using` `System;` `class` `GFG {` ` ` `// Function to find number of triangles` ` ` `public` `static` `int` `noOfTriangles(` `int` `n)` ` ` `{` ` ` `return` `(n * (n + 2) * (2 * n + 1) / 8);` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `Main(String[] args)` ` ` `{` ` ` `int` `n = 3;` ` ` `Console.Write(noOfTriangles(n));` ` ` `}` `}` |

## Javascript

`<script>` `// Javascript implementation of the` `// above approach` `// Function to find the` `// number of triangles` `function` `noOfTriangles(n)` `{` ` ` `return` `Math.floor(n * (n + 2)` ` ` `* (2 * n + 1) / 8);` `}` `// Driver Code` `var` `n = 3;` `// Function call` `document.write(noOfTriangles(n));` `</script>` |

**Output:**

13

**Time Complexity:** O(1)**Auxiliary Space:** O(1)

Attention reader! Don’t stop learning now. Get hold of all the important mathematical concepts for competitive programming with the **Essential Maths for CP Course** at a student-friendly price. To complete your preparation from learning a language to DS Algo and many more, please refer **Complete Interview Preparation Course****.**