I was just looking at the serial numbers for a number of things in my collection, and there are a number of WEIRD coincidences...
HP 82181 X Memory sn8444
HP 82181 X Memory sn8445
HP 82181 X Memory sn8446
HP 82181 X Memory sn8522
HP 82181 X Memory sn8523
HP 82182A Time Module sn2220
HP 82182A Time Module sn2221
I'm sure these serial numbers just refer to year and week of manufacture, rather than being serial numbers per se, but it is interesting that I have so many that for a series, especially the three X Memory modules!