I'm always looking to collect CU notes for my block collection and for some fancy district sets. I have been putting together CU district sets for years with the same end numbers in the serial number. Lately I've been collecting any CU bills I can get with the same triple or quad ending numbers. If you can get CU bills at your bank and want to make a trade let me know. I usually trade $5-$15 at a time, I keep it small and it doesn't break my budget.