What is the format for FAA aircraft N numbers?

There are three forms you can have a N-number. One way is N then one-five numbers (N12345). The second way is N then one-four numbers followed by one letter (N1234A). The last way is N then one-three numbers followed by two letters (N123AB). Also a N-number may not begin with zero after the N. For example N03452 is not valid. N-numbers N1-N99 are reserved for the FAA.