# is the transaction number, it is incremented for each depot changing operation and is incrementing continuously.
The difference between Real Version and Virtual Version is described in AccuRev help (%PROGRAMFILES%/AccuRev/doc/WebHelp/InDepth_Real_and_Virtual_Versions.htm)
I found the AccuRev documentation to be confusing. Here is what I've come to understand:
# is the transaction number. Every action in an AccuRev depot is assigned a unique (auto-incrementing) transaction number. When multiple files are affected in one action, they share the transaction number.
"Virtual version" is the stream name (or number), followed by a slash, followed by the count of which version it is on that stream. So, the first version of helloworld.c on the IntegrationStream is IntegrationStream/1, or perhaps a number like 123/1. I don't know why sometimes a number is shown instead of the stream name. If multiple changes have been kept on the file in another stream and the file with multiple changes is finally promoted to this stream (IntegrationStream), this increments the number only by one. So the next version visible on this stream would be IntegrationStream/2 (or 123/2).
The "real version" refers to the first time that revision of the file was seen in the depot. This would be when the original keep operation was performed in someone's workspace. So if the version of the file seen in IntegrationStream/2 is the result of a keep in Proj_jsmith/7 which was promoted up to IntegrationStream, then the real version shows up as Proj_jsmith/7.
The ancestor, merge and patch version, if applicable, can be best understood by switching to "version browser mode" where the ancestor, merge, and patch lines are shown. Those columns in the lower panel grid refer to the versions that are associated to the given version of a file by preceding it as an ancestor or by being the source of a merge or patch.