In this post, we will learn how to find the sum of natural numbers in Python using for loop, while loop, and function with detailed explanations and examples.

But before we jump into the programming part first let’s understand what are natural numbers.

## What are Natural Numbers?

The natural numbers are collection of positive numbers starting from 1 to ∞

For Example 1,2,3,4,5,6,7,8,9… etc are natural numbers

## Algorithm

1. Take input from the user (`num`).
2. take one variable `total` to store the sum of all the natural numbers, initially set to zero (`total = 0`).
3. Using for-loop iterate from 1 to num (`for i in range(1, num+1)`).
4. Inside for-loop do `total+=i`
5. At the end outside of the loop print `total`.

Now, based on the above explanation, we understand what natural numbers are and how to implement a program to calculate their sum in Python. So, let’s now dive into the programming part.

## Sum of natural numbers in Python Using for loop

Few programming concepts you have to know before writing this program:

### Source Code

``````num = int(input("Enter a number: "))

total = 0
for i in range(1,num+1):
total+=i

print(f"Sum of 1 to {num} natural numbers is : {total}")``````

### Output

``````Enter a number: 10
Sum of 1 to 10 natural numbers is : 55``````

## Sum of natural numbers in Python Using while loop

Before writing this program few programming concepts you have to know:

NOTE: For this program, the above algorithm is being used, only the syntax has been changed.

### Source Code

``````num = int(input("Enter a number: "))

total = 0
i = 0
while i<=num:
total+=i
i = i+1

print(f"Sum of 1 to {num} natural numbers is : {total}")``````

### Output

``````Enter a number: 20
Sum of 1 to 20 natural numbers is : 210``````

## Sum of natural numbers in Python Using function

Before writing this program few programming concepts you have to know:

### Source Code

``````def sum_n(n):
total = 0
for i in range(1, n+1):
total+=i
``````Enter a number: 5