[ci5er]

You could always try...

  - https://www.facebook.com/1
  - https://www.facebook.com/2
  - https://www.facebook.com/3

My guess (and there may even be apocrypha about it), is that these were old registration test accounts that didn't survive the first Zuckerbergian purge.

[leebyron]

Correct. SQL auto increment keys plus test accounts resulted in Zuck being 4.