By way of analogy with the eban numbers, aban numbers are defined as numbers whose English names do not contain the letter "a" (i.e., "a" is banned). Note that this definition is imprecise insofar as special names are sometimes assigned to a few large numbers that do not follow the usual rules for the naming of such numbers.
Since the word "thousand" contains an "a" but no smaller numbers do, the numbers 1-999, 
-
, 
-
, ... etc. are aban numbers.
