General formula to find nth term is needed.

Job ID: 36562161

Budget: $10 – $30 USD

Formula Wanted !
Sum of numbers

(x times y) - (z)

X=13
Y=8
Z=5

1-99
2-787
3-6291
4-50323
5-402579
6-2220627
7-25765011
8-.........
9-.........

Question: how can I calculate 50th without writing down from 1st ?
I will pay if you can find me the formula!

Related categories: Data Processing Data Entry Excel Statistics Mathematics