UA block would be 99999999 notes(156.25 runs) less spoilage replaced by star notes, according to the text (ODonnell's book) UA is one of the most common blocks. you can pick one up in choice uncirculated for about ten bucks. When the BEP stopped printing Silver certificates they announced that there were about 600 trillion notes outstanding that had not been redeemed for silver as of June 1967.