A Cullen Number is a number of the form is 2^{n} * 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 2^{n}, then multiply the result with n and finally returns (1 << n)*n + 1.

## C++

`// C++ program to find Cullen number ` `#include <bits/stdc++.h> ` `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

`<?php ` `// PHP program to ` `// find Cullen number ` ` ` `// function to find n'th ` `// cullen number ` `function` `findCullen(` `$n` `) ` `{ ` ` ` `return` `(1 << ` `$n` `) * ` `$n` `+ 1; ` `} ` ` ` ` ` `// Driver code ` ` ` `$n` `= 2; ` ` ` `echo` `findCullen(` `$n` `); ` ` ` `// This code is contributed by ajit ` `?> ` |

**Output:**

9

**Properties of Cullen Numbers:**

- Most of the Cullen Numbers are composite numbers.
- 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

This article is contributed by DANISH_RAZA. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.