Alien Registration Number, Explained: The U.S. Immigration A# - Boundless
https://www.boundless.com/immigration-resources/what-is-an-alien-registration-number/
WEBYour A-number is always a 7, 8, or 9-digit number. Your USCIS case number, on the other hand, is a 13-character code beginning with 3 letters (such as “MSC” or “EAC”) and then 10 numbers. Confusingly, you’ll sometimes see “USCIS number” or “USCIS#” — without the “case” — used to refer to your Alien Registration Number.
DA: 4 PA: 18 MOZ Rank: 10