# The sum of the first n natural numbers

1
15
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The sum of the first n natural numbers are written as

1=1
1+2=3
1+2+3=6
1+2+3+4=10
1+2+3+4+5=15

What is the formula to calculate this sum:

Logic Source-http://www.9math.com/book/sum-first-n-natural-numbers

## simple logic

1. Take the number from user.
2. Add them up one by one

## Implementation

1. Take the number from user.
2. Add them up one by one
//after taking input from user convert that to integer

private static void calculate_sum(int i) {
int sum=0;
int num=i;
for (int j=1;j<=num;j++)
{
sum+=j;
}
System.out.print(sum);
}

But as per mathematics there is one formula to calculate that

## Formula logic

1. Take the number from user.
2. Add them up one by one

## Implementation

1. Take the number from user.
2. put the formula
//after taking input from user convert that to integer

private static void calculate_sum(int i) {
//Initialize sum as 1 and a temp variable called num
int sum=1;
int num=i;
// implement formula
sum=i*(i+1);
sum=sum/2;
System.out.print(sum);

}
}

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