Is city of ember a trilogy?

Everyone's opinion is different, but I happen to like it. Here is the plot: The City of Ember is an underground city that is slowly dying. It has blackouts that last longer every time one happens, and everyone starts to worry. Two friends try to find a way to save the city before the lights go out for good. If you like mystery, friendship, and adventure try them out. There are also a few more books in the series and are equally good.