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# Program to find Cullen Number

• Last Updated : 23 Mar, 2021

A Cullen Number is a number of the form is 2n * n + 1 where n is an integer. The first few Cullen numbers are 1, 3, 9, 25, 65, 161, 385, 897, 2049, 4609 . . . . . .
Examples:

```Input : n = 4
Output :65

Input : n = 0
Output : 1

Input : n = 6
Output : 161```

Below is implementation of formula. We use bitwise left-shift operator to find 2n, then multiply the result with n and finally returns (1 << n)*n + 1.

## C++

 `// C++ program to find Cullen number``#include ``using` `namespace` `std;` `// function to find n'th cullen number``unsigned findCullen(unsigned n)``{``    ``return` `(1 << n) * n + 1;``}` `// Driver code``int` `main()``{``    ``int` `n = 2;``    ``cout << findCullen(n);``    ``return` `0;``}`

## Java

 `// Java program to find Cullen number``import` `java.io.*;` `class` `GFG {``    ``// function to find n'th cullen number``    ``static` `int` `findCullen(``int` `n)``    ``{``        ``return` `(``1` `<< n) * n + ``1``;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `n = ``2``;``        ``System.out.println(findCullen(n));``    ``}``}` `// This code is contributed by vt_m.`

## Python3

 `# Python program to``# find Cullen number` `# Function to calculate``# Cullen number``def` `findCullen(n):` `    ``# Formula to calculate``    ``# nth Cullen number``    ` `    ``return` `(``1` `<< n) ``*` `n ``+` `1` `# Driver Code``n ``=` `2``print``(findCullen(n))` `# This code is contributed``# by aj_36                `

## C#

 `// C# program to find Cullen number``using` `System;` `class` `GFG {``    ``// function to find n'th cullen number``    ``static` `int` `findCullen(``int` `n)``    ``{``        ``return` `(1 << n) * n + 1;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `n = 2;``        ``Console.WriteLine(findCullen(n));``    ``}``}` `// This code is contributed by vt_m.`

## PHP

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## Javascript

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Output:

`9`

Properties of Cullen Numbers:

1. Most of the Cullen Numbers are composite numbers.
2. n’th Cullen number is divisible by p = 2n – 1 if p is a prime number of the form 8k – 3.

Reference: https://en.wikipedia.org/wiki/Cullen_number
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