Need use the exponential interpolation of a sequence of numbers to project future numbers

I have a business situation as follows: My business offers a services that can be qualified on a weekly basis with a number. The number decreases over time to the number 1. It is expected that the number will decrease as an exponential decay function. For example, 128, 64, 32, 16, 8, 4, 2, 1. (a crude example but exponential decay nonetheless). Each week we get a new number. An exponential function requires three points, so, after the third week, we should be able to predict the future values. Of course, once there are 4 points, we will have to interpolate the best fit exponential function. My goal is to use all the numbers available to project the most accurate future results. For example, if the numbers were 128, 64, 32...we would expect 16, 8, 4, etc. However, if the numbers were 128, 65, 32, we would expect something slightly different.

There are two issues in achieving my goal:
1) I need to use all the numbers available to me, which will vary.
2) I need to use an interpolation function in the background (no graphs).

The layout will be as follows:
Each row will contain a sequence of numbers, and each week we will progress to the next column. I want there to be a function (or some VBA) that automatically fills in the future rows that have not been reached. Each time we move over to the next column, we will replace the function (which was projecting a value) with a static value (based on actual performance) and the future values will update (based on newly projected performance).

Thank you in advance, to anyone savvy enough to help me with this.

Best,
Adam

Made some progress here. So it turns out that the GROWTH function works perfectly. I am using it as follows:

=growth([list of values], [separate static row of consecuitive integers], [the next integer from that static row])

This works well as giving me the next value in the row, however, I need to project all the next values. So, in the array, I can you "#" and drag across. The issue with this is two fold. First, I need to drag down since I have many rows that I will be doing this with, and if I drag down with the "#" they won't fill. ie. I need them static on the horizontal fill, but dynamic on the vertical fill. The other issue is that when I add another column of static values (because we are in a new week), I need all those arrays that I filled to consider the new array size.

Thanks.

Aaaand. One more issue. This function decays exposentially to 0, but the lowest number should be one. This is easy to fix mathematically. All I need to do is subtract 1 from all the y values, use the function, and then add 1 to the result. But I am dealing with an array, and I need the array put into the function to be an array of values one less than the array that is available on the sheet.

Thanks.