Going off this site

The Present Value and Future Value of an Annuity; Annuity Due, Ordinary Annuity; Time Value, with Formulas and Examples; Discount Rate

I am trying to figure out how annuities and interest works.

So I decided to Calculate this:

100 * ((1+.005)120 -1)/.005

FVOA =

A * (1 + i)n - 1 / i

A= Amount

i= Interest

n= number of periods

According to the website the answer is $36,387.93

But when I put it in on my calculator, the answer is $16,387.93

My answer is exactly $20,000 less than the answer the site gives.

Any reason for this?