Pattern Recognition Puzzle - What would 100 correspond to? There is a mathematical puzzle I saw this morning that I am having trouble with. 
Seemed easy initially but couldn't crack the code. Can anybody please help work out the answer for the below?
Given the following pattern, find out 1) What is the mathematical formula used to derive the number of the right from the number on the left? 2) What number can be derived from 100 when applying the same formula?
2 => -1
3 => -2
6 => 3
8 => 3
14 => 6
16 => 9
20 => 14
22 => 13
37 => 26
40 => 35
48 => 38
50 => 45
51 => 43
56 => 48
58 => 48
60 => 55
61 => 53
91 => 82
100 => ?
101 => 88


I graphed it here. It seems pretty linear, and if you make a line of best fit, 100 would correspond to about 90. Although I can't seem to figure out the algorithm, hopefully the graph helps.

