Hacker News Reader

Source, Dustin Moskovitz: 1-3 were accounts used to test registration. Evidently it only took Mark 3 tries to clear the bugs. Link: http://qr.ae/NMpX6 (Does not require login)

There's even a https://www.facebook.com/NaN :)

Also: https://www.facebook.com/window.location.href

For some reason https://www.facebook.com/undefined is different from a regular 404 like https://www.facebook.com/null

I see Zuck as #1, Moskowitz as #3 and so on...

Click on the picture, it links to "facebook.com/4" (=zuckerberg), etc. There are several gaps in between the first 50 ID numbers. Probably some early test/fake accounts as well as people who deleted/deactivated their account. Eduardo Saverin (co-founder) has id 41 and Joe Green has 42.