# Program to find Cullen Number

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

```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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

 ` `

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.

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Improved By : jit_t

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