Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines? In jet engines, I read that thrust is related to the fuel flow rate, whereas in turboprop engines power produced is related to the fuel flow rate. What is the reason and brief math behind this?
Ultimately what you want from all three types of engines is quantification of thrust available to push an airplane through the sky. The turbofan/jet engines are self contained and produce thrust directly but a turboprop engine requires the addition of a propeller, which may have differing characteristics based on the installation. 

Since thrust is not known for a turboprop until its installation has been determined, manufacturers instead quantify the power available to drive a prop. This allows engines to be compared so that an airframe manufacturer can make the proper selection.

Fuel flow is then related to either thrust or power as a measure of efficiency, depending on type of engine. There is generally no published mathematical relationship between power and thrust for a given engine. It is not needed for turbofans/jets and not possible to determine at time of manufacture for turboprops.