I've looked on the Stack Exchange site and the Data Explorer, and I can't seem to find the number of unique users on the entire stack exchange system. It maybe that these numbers don't exist, but it seems like you just have to count the number of valid unique open-ids across every stack exchange site and you have it. Maybe I'm being silly and these numbers are easy to find.
Can anyone help me to find a query or statistic page that gives me this info?
Edit, simplification: Where can I find the closest count of the total number of people on planet earth who have a single stack exchange account?