# Sum of natural numbers using recursion

Given a number n, find sum of first *n* natural numbers. To calculate the sum, we will use a recursive function recur_sum().**Examples :**

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Input : 3 Output : 6 Explanation : 1 + 2 + 3 = 6 Input : 5 Output : 15 Explanation : 1 + 2 + 3 + 4 + 5 = 15

Below is code to find the sum of natural numbers up to n using recursion :

## C++

`// C++ program to find the` `// sum of natural numbers up` `// to n using recursion` `#include <iostream>` `using` `namespace` `std;` `// Returns sum of first` `// n natural numbers` `int` `recurSum(` `int` `n)` `{` ` ` `if` `(n <= 1)` ` ` `return` `n;` ` ` `return` `n + recurSum(n - 1);` `}` `// Driver code` `int` `main()` `{` ` ` `int` `n = 5;` ` ` `cout << recurSum(n);` ` ` `return` `0;` `}` |

## Java

`// Java program to find the` `// sum of natural numbers up` `// to n using recursion` `import` `java.util.*;` `import` `java.lang.*;` `class` `GFG` `{` ` ` `// Returns sum of first` ` ` `// n natural numbers` ` ` `public` `static` `int` `recurSum(` `int` `n)` ` ` `{` ` ` `if` `(n <= ` `1` `)` ` ` `return` `n;` ` ` `return` `n + recurSum(n - ` `1` `);` ` ` `}` ` ` ` ` `// Driver code` ` ` `public` `static` `void` `main(String args[])` ` ` `{` ` ` `int` `n = ` `5` `;` ` ` `System.out.println(recurSum(n));` ` ` `}` `}` `// This code is contributed by Sachin Bisht` |

## Python

`# Python code to find sum` `# of natural numbers upto` `# n using recursion` `# Returns sum of first` `# n natural numbers` `def` `recurSum(n):` ` ` `if` `n <` `=` `1` `:` ` ` `return` `n` ` ` `return` `n ` `+` `recurSum(n ` `-` `1` `)` `# Driver code` `n ` `=` `5` `print` `(recurSum(n))` |

## C#

`// C# program to find the` `// sum of natural numbers` `// up to n using recursion` `using` `System;` `class` `GFG` `{` ` ` `// Returns sum of first` ` ` `// n natural numbers` ` ` `public` `static` `int` `recurSum(` `int` `n)` ` ` `{` ` ` `if` `(n <= 1)` ` ` `return` `n;` ` ` `return` `n + recurSum(n - 1);` ` ` `}` ` ` ` ` `// Driver code` ` ` `public` `static` `void` `Main()` ` ` `{` ` ` `int` `n = 5;` ` ` `Console.WriteLine(recurSum(n));` ` ` `}` `}` `// This code is contributed by vt_m` |

## PHP

`<?php` `// PHP program to find the` `// sum of natural numbers` `// up to n using recursion` `// Returns sum of first` `// n natural numbers` `function` `recurSum(` `$n` `)` `{` ` ` `if` `(` `$n` `<= 1)` ` ` `return` `$n` `;` ` ` `return` `$n` `+ recurSum(` `$n` `- 1);` `}` `// Driver code` `$n` `= 5;` `echo` `(recurSum(` `$n` `));` `// This code is contributed by Ajit.` `?>` |

## Javascript

`<script>` `// JavaScript program to find the` `// sum of natural numbers` `// up to n using recursion` `// Returns sum of first` `// n natural numbers` `function` `recurSum(n)` `{` ` ` `if` `(n <= 1)` ` ` `return` `n;` ` ` `return` `n + recurSum(n - 1);` `}` `// Driver code` `let n = 5;` `document.write(recurSum(n));` `// This code is contributed by mohan` `</script>` |

**Output :**

15