Rectangular (or Pronic) Numbers

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 ``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

 ` `

Javascript

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Output:

`42`

Time complexity: O(1) since performing constant operations

Space complexity: O(1) since using constant space for variables

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