
PlanetMath: factorial base 
  it is obvious that factorial base is unambiguous, though it has the potential to use an infinite amount of distinct digits even as the less significant place values are limited in what values they can contain. 
  This is version 4 of factorial base, born on 20060523, modified 20070227. 
  "The factorial base representations are unambiguous as long as the maximum allowed digit for a given place value is not exceeded (e.g., the least significant digit can only be 0 or 1, while the most significant digit in an 7digit factorial base number has to be in the range 0 to 7). 
 planetmath.org /encyclopedia/FactorialBase.html (462 words) 