The numbers that can be arranged to form a rectangle are called Rectangular Numbers (also known as Pronic numbers). The first few rectangular numbers are:

0, 2, 6, 12, 20, 30, 42, 56, 72, 90, 110, 132, 156, 182, 210, 240, 272, 306, 342, 380, 420, 462 . . . . . .

Given a number n, find n-th rectangular number.

Examples:

Input : 1 Output : 2 Input : 4 Output : 20 Input : 5 Output : 30

The number 2 is a rectangular number because it is 1 row by 2 columns. The number 6 is a rectangular number because it is 2 rows by 3 columns, and the number 12 is a rectangular number because it is 3 rows by 4 columns.

If we observe these numbers carefully, we can notice that n-th rectangular number is **n(n+1)**.

## C++

`// CPP Program to find n-th rectangular number ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Returns n-th rectangular number ` `int` `findRectNum(` `int` `n) ` `{ ` ` ` `return` `n * (n + 1); ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `int` `n = 6; ` ` ` `cout << findRectNum(n); ` ` ` `return` `0; ` `} ` |

## Java

`// Java Program to find n-th rectangular number ` `import` `java.io.*; ` ` ` `class` `GFG { ` ` ` ` ` `// Returns n-th rectangular number ` ` ` `static` `int` `findRectNum(` `int` `n) ` ` ` `{ ` ` ` `return` `n * (n + ` `1` `); ` ` ` `} ` ` ` ` ` `// Driver code ` ` ` `public` `static` `void` `main(String[] args) ` ` ` `{ ` ` ` `int` `n = ` `6` `; ` ` ` `System.out.println(findRectNum(n)); ` ` ` `} ` `} ` ` ` `// This code is contributed by vt_m. ` |

## C#

`// C# Program to find n-th rectangular number ` ` ` `using` `System; ` ` ` `class` `GFG { ` ` ` ` ` `// Returns n-th rectangular number ` ` ` `static` `int` `findRectNum(` `int` `n) ` ` ` `{ ` ` ` `return` `n * (n + 1); ` ` ` `} ` ` ` ` ` `// Driver code ` ` ` `public` `static` `void` `Main() ` ` ` `{ ` ` ` `int` `n = 6; ` ` ` `Console.Write(findRectNum(n)); ` ` ` `} ` `} ` ` ` `// This code is contributed by vt_m. ` |

## Python

`# Python3 Program to find n-th rectangular number ` ` ` `# Returns n-th rectangular number ` `def` `findRectNum(n): ` ` ` `return` `n` `*` `(n ` `+` `1` `) ` ` ` `# Driver code ` `n ` `=` `6` `print` `(findRectNum(n)) ` ` ` `# This code is contributed by Shreyanshi Arun. ` |

## PHP

`<?php ` `// PHP Program to find n-th ` `// rectangular number ` ` ` `// Returns n-th rectangular ` `// number ` `function` `findRectNum(` `$n` `) ` `{ ` ` ` `return` `$n` `* (` `$n` `+ 1); ` `} ` ` ` ` ` `// Driver Code ` ` ` `$n` `= 6; ` ` ` `echo` `findRectNum(` `$n` `); ` ` ` `// This code is contributed by ajit ` `?> ` |

Output:

42

Check if a given number is Pronic | Efficient Approach

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