Seems like a reasonable description of numbers which only appear once in a google search. Try finding one shorter than nine digits, and you’ll be at it a while. The average number of matches for an eight digit number appears to be between 5 and 10, which means I have no trouble believing that their index really is frikkin huge. It’s also a great way to find a page almost randomly… maybe Google should have an "I’m feeling REALLY lucky" button for those occasions when you don’t even know what you’re searching for in the first place.