# Sum of N Natural Numbers in Python

We have to develop a Python program to find the sum of N natural numbers. Sum of natural number N as given as sum = 1+2+3+4+5+….+(N-1)+N. We can use the while or for loop to write the program. We can also develop a Python program without using the loop.

Examples:-
1+2+3+4+5+6 = 21
1+2+3+4+5+6+7+8+9+10 = 55

## Python Program to Find Sum of N Natural Numbers

This python program using a while loop to find the sum of natural numbers. We will take a natural number while declaring the variables. Python program to find the sum of n natural numbers using while loop and finally, the result will be displayed on the screen.

``````# Python program to find sum of n natural numbers

# take input
num = int(input('Enter a number: '))

# find sum of natural number
sum = 0
x = 1
while x <= num:
sum += x
x += 1

# display result
print('The sum of natural number =', sum)``````

Output for the different input values:-

Enter a number: 5
The sum of natural number = 15

Enter a number: 10
The sum of natural number = 55

Enter a number: 239
The sum of natural number = 28680

## Python Program to Find Sum of N Natural Numbers using For loop

In the previous program, we will use the while loop but in this program, find the sum of n natural numbers using for loop.

``````# Python program to find sum of n natural numbers

# take input
num = int(input('Enter a number: '))

# find sum of natural number
sum = 0
for x in range (1, num+1):
sum += x

# display result
print('The sum of natural number =', sum)``````

Output:-

Enter a number: 25
The sum of natural number = 325

## Find the Sum of N Natural Numbers using Function

We can also take the help of a user-defined function. A function is a block of code that performs a specific task.

``````# Python program to find sum of n natural numbers using function

def findSum(num):  #user-defined function
sum = 0
x = 1
while x <= num:
sum += x
x += 1
return sum

# take input
num = int(input('Enter a number: '))

# display result
print('The sum of natural number =', findSum(num))``````

Output:-

Enter a number: 83
The sum of natural number = 3486

## Sum of N Natural Numbers using Recursion

We can also use the recursion technique to find the sum of n natural numbers. A technique of defining the method/function that contains a call to itself is called recursion. The recursive function/method allows us to divide the complex problem into identical single simple cases that can handle easily. This is also a well-known computer programming technique: divide and conquer.

``````# Python program to find sum of n natural numbers using recursion

def findSum(num):  #user-defined function
if(num == 0):
return num
else:
return (num + findSum(num - 1))

# take input
num = int(input('Enter a number: '))

# display result
print('The sum of natural number =', findSum(num))``````

Output:-

Enter a number: 325
The sum of natural number = 52975

Enter a number: 1000
RuntimeError: maximum recursion depth exceeded in comparison

## Other Efficient Program

This python program is very smallest and easy to understand. In this program, We will use only one formula to find the sum of natural numbers.

Formula:- n * (n+1) / 2

Examples:-
1+2+3+4+5+6 = 6 * (6+1) / 2 = 3 * 7 = 21
1+2+3+4+5+6+7+8+9+10 = 10 * (10+1) / 2 = 5 * 11 = 55

``````# Python program to find sum of n natural numbers

def findSum(num):  #user-defined function
return num * (num+1) / 2

# take input
num = int(input('Enter a number: '))

# display result
print('The sum of natural number =', findSum(num))``````

### Another Program

The above program causes an overflow, even if the result is not beyond the integer limit. We can avoid overflow up to some extent by doing division first.

``````# Python program to find sum of n natural numbers

def findSum(num):  #user-defined function
if (num % 2 == 0) :
return (num/2) * (num+1)

# If num is odd, (n+1) must be even
else :
return  ((num+1) / 2) * num

# take input
num = int(input('Enter a number: '))

# display result
print('The sum of natural number =', findSum(num))``````

Also See:- Sum of Digits of a Number in Python

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