# Rectangular (or Pronic) Numbers

• Difficulty Level : Easy
• Last Updated : 21 Jun, 2022

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

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## 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

Check if a given number is Pronic | Efficient Approach
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