## __Write a program to find sum of n natural number in O(1)__

Given a number , write a program to find the sum of natural numbers up to n . For this we will use a simple formula .

Sum of natural number up to n :- **(n*(n+1)) /2**

**Sample input :**

10

**Sample output:**

55

__Write a program to find sum of n natural number in O(1)__

The objective of the code is to find the sum of n natural numbers in O(1) time . Value of n is given by user .

__Code(C):-__

#include<stdio.h>

int main()

{

int n,sum;

printf("Enter the number ");

scanf("%d",&n);

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

printf("sum is %d",sum);

}

**Output:-**

Enter the number

10

sum is 55

__Code(C++):-__

#include <iostream>

using namespace std;

int main()

{

int n,sum;

cout<<"Enter the number ";

cin>>n;

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

cout<<"sum is "<<sum;

return(0);

}

**Output:-**

Enter the number

10

sum is 55

__Code(Python):-__

print("Enter the number ")

n=int(input())

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

print(f"sum is {sum}")

**Output:-**

Enter the number

10

sum is 55

**Sum of n natural numbers by using loop :- click here**

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