Yes. You can even get a 3 or 4 character reserve plate by requesting it, such as the "sandwich plate" in the format of A1A, 1A1, A11A, A 1111, 1111 A, 123 A, or A 123 - or 11111. I like 11111 because serial wise they are actually lower than anything that includes a letter, historically. I have one on my car, should come up if you go on my profile.
The lottery plates that you can only get by wining the lottery are of the formats: 1, 11, 111, 1111, 1 A, 11 A, A 1, A 11, or A - the last one, being a single letter, does not have a numeral to correspond to the expiration month, so it would expire on December 31.
Keeping in mind of course that passenger plates expire from January to October - 1 for JAN, zero for OCT. November are vanity plates and December is for commercials, motorcycle plates, and reserve single-letter plates.