Course, the sum of the first 'n' natural numbers is: n x (n+1) / 2
This can be proved by induction:
If the sum of 'n' natural numbers is: n x (n+1) / 2 then the sum to n+1 =
n x (n+1) / 2 + (n + 1)
= (n2 + n)/2 + (n + 1)
= n2 + n / 2 + (2n + 2 / 2)
= (n2 + 3n + 2) / 2
= (n + 1) (n + 2) / 2
QED
That's why I get all the girls