Python Program to Find the Sum of Natural Numbers

In the program below, we've used an if else statement in combination with a while loop to calculate the sum of natural numbers upto num.

Source Code

# Python program to find the sum of natural numbers up to n where n is provided by user

# change this value for a different result
num = 16

# uncomment to take input from the user
#num = int(input("Enter a number: "))

if num < 0:
   print("Enter a positive number")
else:
   sum = 0
   # use while loop to iterate un till zero
   while(num > 0):
       sum += num
       num -= 1
   print("The sum is",sum)

Output

The sum is 136

Note: To test the program, change the value of num.

Here, we store the number in num and display the sum of natural numbers up to that number. We use while loop to iterate until the number becomes zero.

We could have solved the above problem without using any loops using a formula directly.

Your turn: Modify the above program to find the sum of natural numbers using the formula below.

n*(n+1)/2

For example, if n = 16, the sum would be (16*17)/2 = 136.