In the attached workbook is a table which is meant to determine the projected increase in mite populations for a given variable over 12 months. The table below is simply a copy of the table within the workbook. I am trying to calculate how the supplied result was achieved. My best guess and its only a guess, to calculate the Overall fold increase is to use the formula 

 =Round(Month+ (Month*0.021),0)
Which is only accurate for the first 6 months then it goes astray.

Month r Value Overall Fold increase Supplied Result
1 0.021 =Round(A2+(A2*B2),0) 1
2 0.021 2
3 0.021 4
4 0.021 7
5 0.021 12
6 0.021 23
7 0.021 44
8 0.021 82
9 -0.005 154
10 -0.005 133
11 -0.005 114
12 -0.005 98
13 -0.005 85

Could someone help me understand how to construct the correct formula please?