Why are USPTO patent applications numbered XX/XXX,XXX?

Question

USPTO patent applications are numbered XX/XXX,XXX. Why the slash? I.e., why not XX,XXX,XXX? Is it to distinguish from USPTO patent numbers, or is there some other reason?

Answer 1

An official version of a patent number does not have any commas. If you looked up an application in Public Pair, before it was shut down, commas would screw up the search.

Therefore the slash is needed to demarcate the series. Other than provisional applications and non-provisional applications having different series, I do not know the purpose of the series.

The commas are merely there for readability in some contexts, like in currency.