I got stuck aswell on this puzzle,
I'm from the netherlands where we use Euros.
Though if the game would just include coins with numbers on them it would be much easier to solve.
First i thought the puzzle was going for the fibbonaci sequence, but then i found out something more... digital, anyways be sure to localize those puzzles.
The fact that we can actually speak/read english doesnt necessarily mean we know how to recognise foreign currencies.
Also this really broke the "flow" of the game since i had to get out to find info on US coinage, then start a account here to type this post...