Exponential stairs

Hi,

I would like to make some kind of exponential stairs base on the blondel equation:

2 x riser + tread = step length

the first step would be  : How to write an exponential function giving an initial value and ending by 0

I try to divide a curve , the first segment would be 17cm and the last 0 using an Eval and Graphmaper to get the segments in between.

thank you for your help

Anjy