Hey guys, in this blog we will see a Python Program to Find the Sum of Natural Numbers.

## Example 1: Using While Loop

# Python Program to Find the Sum of Natural Numbers num = int(input("Enter a positive number -> ")) if num < 0: print("Enter a positive number") else: sum = 0 # use while loop to iterate until zero while(num > 0): sum += num num -= 1 print("The sum is ->", sum)

**Output**

Enter a positive number -> 4 The sum is -> 10

Enter a positive number -> 5 The sum is -> 15

Enter a positive number -> 6 The sum is -> 21

- In this way, we have simply declared a sum variable and we keep on adding the number to this variable.
- Also simultaneously we are reducing our original number in every iteration.
**Suppose the user inputs 4, our program will add 4 to sum which is currently 0, and reduce our org number 4 to 3, now in the next iteration our program will add 3 to sum, now sum becomes 7 and num becomes 2 and in this way when num becomes 0, our loop will break.**

## Example 2: Using the formula

**sum = n*(n+1)/2**

# Sum of natural numbers up to num num = int(input("Enter a positive number -> ")) if num < 0: print("Enter a positive number") else: sum = (num*(num+1))//2 print("The sum is ->", sum)

**Output**

Enter a positive number -> 8 The sum is -> 36

Enter a positive number -> 9 The sum is -> 45

Enter a positive number -> 10 The sum is -> 55

- This is the easiest way of calculating the sum of all natural numbers till a positive number.
**Suppose n=8, so the sum of all natural numbers till 8 will be (8*9)/2 which equals 36.**

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