to add 1 to n number

n(n+ 1)

this formula helps us to adding 1 to n number easily

for instance 1 + 2 + 3 + 4 + 5+ 6  +7 + 8 + ..... + 25 = 325

by use formula

n = 25

25 * 26 / 2 = 325

this formula is can be work with it in the big sequence start from 1

i think now it is very easy