Question

sum of n natural numbers formula 

Answer 1

the formula is n(n+1)/2
for example 1+2+3+4=3+7=10
n=4

4(4+1)/2
=4(5)/2
=20/2
=10

Answer 2

let the no of natural nos be n
so the formula is 
$\frac{n(n+1)}{2}$