Need a tricky exponential formula.

I want to do the following.

I want to add X + X (the same again) + a Growing multiply-able % of the same X.
Then the Result of this + X (the same) + double the % of X.

So if i got 100 as X
The a cell adds 100+100 + say 5% of 100 = 200 + 5 = 205
However for the next cell i want this to add the result + 10% instead of 5% of the 100.

So far I can do it by saying =CELL + (SAMECELL*1.05)
But that way i have to tweak the current modifier (1.05 [5%]) for every cell.

I bet there is a fancier way of doing that...

Anyone?

P.S.

Solutions:
1. See Ben's example in post 2.

2.

Here's the entire thing so anyone can recreate it:

C18 is 100 (Base number)
B18 is 20 (the %)
D18 is =C18*B18% (that shows you how much 20% is off 100)

C1 =C18
C2 =(C1+C$18)+ROWS(C$2:C2)*D$18
C3 =(C2+C$18)+ROWS(C$2:C3)*D$18
C4 =(C3+C$18)+ROWS(C$2:C4)*D$18
C5 =(C4+C$18)+ROWS(C$2:C5)*D$18
C6 =(C5+C$18)+ROWS(C$2:C6)*D$18

However if you don't want a cell to view the result you get off your Base and % you can skip it by replacing the last bit *D$18 with *(C18*B18%) and that is that.

Rows counts the number of cells in a specified range, in this case from A4 to A21. Depending on which of the two cells on the end of the range you lock, the formula auto adjusts to count 1 more or less cell in each following cell you paste it. Allowing you to work with both exponential increase or decrease.

And as Ben was said you add a $ when you want the cell numbers to stay fixed from auto adjustment when you paste formulas elsewhere.

Now all i need is the syntax to actually add % since when I do =100+5% i get "10005.00%" instead of 105. And if i do 100 * 5 % it gives me a 5 as it should.

...Solutions updated in main post...

The added % is exponential.

Rows provides what you take your modifier from B1 in your example, and does so proportionately.

In this case if my % is 20 on my base of 100

I get exactly what i set out to get.

100
220 + 20% off 100
360 +40% off 100
520 +60% off 100
700 etc
900
1120
1360
1620
1900

So the percent growth is exponential - unless my math terminology is way out of whack and this example effect should be called something else other than exponential growth.

Anything else can grow the same way if you tie in the rows right.

Here's the entire thing so anyone can recreate it:

C18 is 100 (Base number)
B18 is 20 (the %)
D18 is =C18*B18% (thats shows you the result off 100*20%)

C1 =C18
C2 =(C1+C$18)+ROWS(C$2:C2)*D$18
C3 =(C2+C$18)+ROWS(C$2:C3)*D$18
C4 =(C3+C$18)+ROWS(C$2:C4)*D$18
C5 =(C4+C$18)+ROWS(C$2:C5)*D$18
C6 =(C5+C$18)+ROWS(C$2:C6)*D$18

Etc. etc.


...
Oddly enough google does 100+20% the other way for less math proficient (;