I am working on a problem set that involves calculating the future value of a series of payments over 18 years. The first year, there is one lump payment and the remaining years there is a lesser payment but remains the same amount paid annually.

When I use the FV function in excel and apply the first lump as PV, and the following identical payments as PMT, I get the answer, however, to cross check my work, I run the NPV function over all the values, then calculate the FV with the NPV, and I am getting a different answer. Any ideas why I may be getting as different answer?