Sum of n Natural Numbers in Python

Program to Find the Sum of First n Natural Numbers

Suppose you want to find the sum of n natural numbers in python. There are multiple ways to find the sum of first n natural numbers. Let's discuss each method one by one.

Using Recursion

We can use recursion to the sum of n natural numbers in python. Let's understand using an example of how to use recursion to find the sum of n natural numbers.

In the below program, we are calculating the sum of the first n natural number using recursion. The sum() method is recursively called in the decreasing order of natural numbers until the natural number becomes equal to 1.

Output:

The sum of the first 5 natural numbers is 15.

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Using For Loop

Let's understand how to use for loop to find the sum of n natural numbers in python

In the below program, we are using a for loop that is iterating on the range of [1-n] and storing the sum in a variable, let's say sum in this case.

Output:

Using Formula

We can find the sum of n natural numbers in python in the time complexity O(1) and the space complexity of O(1). Let's first understand the formula behind this.

The formula is (n*(n+1))/2, where n represents the first n natural numbers.

Let's understand this formula.

Sum of first n natural numbers=(n*(n+1)/2)

Examples:

n=5
Sum=(5*(5+1))/2=(5*6)/2=30/2=15
The sum of the first 5 natural numbers is 15.

Let's understand how to use the above formula using an example.

Output:

The sum of natural numbers up to 5 is 15.

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See Also:

• Numbers in Python.
• Sum of Digits of a Number in Python.
• Sum of Prime Numbers in Python.
• Find the sum of the first n even natural numbers.