Those are the number of times the console.log("Script Activated")
message has been triggered. Chrome automatically groups consecutively identical log messages rather than write it out each one on a new line. This makes it easier to see previous messages that would normally get scrolled off the top of the console too quickly.
In your case, the interval's callback function is triggering the log message every 10 milliseconds, so it's increment that count very quickly because it will occur 100 times a second.
EDIT: In a comment on another answer you asked why setting the interval value to 10000000000 caused the interval to go extremely quickly, rather than once every ~115 days.
This is because the number exceeds the maximum size a signed 32-bit integer can be is aproximately 2.1 billion (2,147,483,647). Once it exceeds that amount, it "wraps" around to the negative numbers. When setInterval()
receives a negative number for the interval milliseconds, it simply rounds the value up to 4 milliseconds. This results in the interval occurring as quickly as possible, about 1000 times a second. I say "about" because there is no guarantee it will go this quickly on slower hardware.