How do you find the sum of n in python?

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

Source Code

# Sum of natural numbers up to num

num = 16

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

The sum is 136

Note: To test the program for a different number, change the value of num.

Initially, the sum is initialized to 0. And, the number is stored in variable num.

Then, we used the while loop to iterate until num becomes zero. In each iteration of the loop, we have added the num to sum and the value of num is decreased by 1.

We could have solved the above problem without using a loop by using the following formula.

n*(n+1)/2

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

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

Python Program to Find the Sum of Natural Numbers

Natural numbers:

As the name specifies, a natural number is the number that occurs commonly and obviously in the nature. It is a whole, non-negative number.

Some mathematicians think that a natural number must contain 0 and some don't believe this theory. So, a list of natural number can be defined as:

See this example:

This example shows the sum of the first 100 positive numbers (0-100)

Output:

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Find the Sum of N Natural Numbers in Python

Given an integer input number, the objective is to sum all the numbers that lay from 1 to the integer input number and print the sum. In order to do so we usually use iteration to sum all the numbers until the input variable number.

Example
Input : number = 5
Output : 15
Explanation : 1 + 2 + 3 + 4 + 5 = 15

Find the Sum of N Natural Numbers

Given an integer value the objective of the code is to sum up all the numbers until the input integer number. To do so we usually use iteration, we iterate through the numbers until the input number is reached while appending the number to the sum variable. Here are some methods to solve the above mentioned problem

• Method 1: Using for Loop
• Method 2: Using Formula
• Method 3: Using Recursion

We’ll discuss the above methods in detail in the sections below.

Method 1: Using for Loop

In this method we’ll use for loops to iterate through all the numbers until the integer input “number” is reached.

Working

For an integer input “number” we do the following

• Initialize the required variables.
• Using for loop iterate from 0 to number+1.
• Meanwhile append the number to sum variable.
• Print the sum variable.

Let’s implement the above logic in Python code.

Python Code

number,sum = 6,0
for i in range(number+1):
  sum+=i
print(sum)

Method 2: Using the Formula

In this method we’ll use the formula for finding the sum of N integers in a series from series and sequences i.e sum = number * ( number + 1 ) / 2 to calculate the sum until the given integer input.

Working

For an integer input “number”  we perform the following steps

• Initialize sum variable as sum = (number * ( number + 1 ) /2 ).
• Print the sum variable.

Let’s implement the above logic in Python Language.

Python Code

number = 6
sum = int((number * (number + 1))/2)
print(sum)

Method 3: Using Recursion

In this method we’ll use recursion to recursively iterate through the number while appending them to the sum variable until the number is reach which here act as the base case. To learn more about recursion, check out Recursion in Python.

Working

For an integer input “number” we do

• Initialize the required variables.
• Define a recursive function with base case as number ==0.
• Set the step recursive call as number + recursum( number – 1 ).
• Call the recursive function recursum() and print the returned value.

Let’s implement the above logic using Python Language.

Python Code

def recursum(number):
  if number == 0:
    return number
  return number + recursum(number-1)
number, sum = 6,0
print(recursum(number))

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Getting Started

• ASCII Table
• Positive or Negative number: C | C++ |  Java | Python
• Even or Odd number: C | C++ | Java | Python
• Sum of First N Natural numbers:  C | C++ | Java | Python
• Sum of N natural numbers:  C | C++ | Java | Python
• Sum of numbers in a given range: C | C++ | Java  | Python
• Greatest of two numbers: C | C++ | Java | Python
• Greatest of the Three numbers: C | C++ | Java | Python
• Leap year or not: C | C++ | Java | Python
• Prime number: C | C++ | Java | Python
• Prime number within a given range: C | C++ | Java | Python
• Sum of digits of a number: C | C++ | Java | Python
• Reverse of a number : C | C++ | Java | Python
• Palindrome number: C | C++ | Java | Python
• Armstrong number : C | C++ | Java | Python
• Armstrong number in a given range : C | C++ | Java | Python
• Fibonacci Series upto nth term : C | C++ | Java | Python
• Find the Nth Term of the Fibonacci Series : C | C++ | Java | Python
• Factorial of a number : C | C++ | Java | Python
• Power of a number : C | C++ | Java | Python
• Factor of a number : C | C++ | Java | Python
• Finding Prime Factors of a number : C | C++ | Java | Python
• Strong number : C | C++ | Java | Python
• Perfect number : C | C++ | Java | Python
• Automorphic number : C | C++ | Java | Python
• Harshad number : C | C++ | Java | Python
• Abundant number : C| C++ | Java | Python
• Friendly pair : C | C++ |   Java | Python

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