How long until compounded return doubles?

I'm probably the millionth person to figure this out, but if you want to know how long a particular compounded rate of return will take to double your original investment, divide 75 by the percentage.

Example: 16% annual return, compounded annually.

Thus: 75 / 16 = 4.6875.

Proof: 1.16 ^ 4.6875 ~= 2.01.