Hi I am new to this forum and I have a question on the cumulative sum function

Year
0 a*1.1^0
1 a*1.1^1 + 1*1.1^0
2 a*1.1^2 + a*1.1^1+a*1.1^0
3 and so on

Is there a formula can put this together? i tried the VBA code. The answer is not correct somehow.

Thanks