Every time I wanted to find out what f-stop numbers existed between the whole  full stops, I had to spend too much time scouring the web for this info.

Now I finally understand how I can generate these numbers myself.

The fstop numbers are powers of the square root of 2. For example,

(√2)^1 = 1.4
(√2)^1.33 = 1.6
(√2)^1.66 = 1.8
(√2)^2 = 2
(√2)^2.33 = 2.2
(√2)^2.66 = 2.5
(√2)^3 = 2.8
(√2)^4 = 4
(√2)^5 = 5.7