TED-Ed: This one weird trick will get you infinite gold | Dan Finkel

A king demands his treasury's gold be tripled, and a magical man helps by using a special bag. The man later returns to claim a promised child, but offers a chance to guess his name. The bag's magic is explained as a function, and a riddle involving the number of coins is solved using logical reasoning.

What is the mathematical concept that the bag's magic resembles?

How many gold coins did the little man ultimately have in his hand?