Python Program to Find Sum of n Natural Numbers

In this tutorial, we will write a simple Python program to calculate the sum of first n natural numbers.

Program to calculate sum of first n natural numbers in Python

In this program we are not using the natural number addition formula n(n+1)/2, instead we are adding the natural numbers using while loop. The user is asked to enter the value of n and then the program calculates the sum of natural numbers upto the entered value n.

# Program published on https://beginnersbook.com

# Python program to calculate the sum of n Natural Numbers

# n denotes upto which number you want to calculate the sum
# for example, if n is 5 then the sum of first 5 natural numbers
num = int(input("Enter the value of n: "))
hold = num
sum = 0

if num <= 0: 
   print("Enter a whole positive number!") 
else: 
   while num > 0:
        sum = sum + num
        num = num - 1;
    # displaying output
    print("Sum of first", hold, "natural numbers is: ", sum)

Output 1:

Enter the value of n: 6
Sum of first 6 natural numbers is:  21

Output 2:

Enter the value of n: 0
Enter a whole positive number!

Output 3:

Enter the value of n: -10
Enter a whole positive number!

Output 4:

Enter the value of n: 20
Sum of first 20 natural numbers is:  210

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