One way to think of this is 
	LLL#### --> LL | L# | ###
	where L={A...Z} and #={0...9} 
since the range of LL is AA to ZZ == 26*26 values == 676 and
the range of L# is A0 to Z9 == 26*10 values == 260 and the
range of ### is 000 to 999 == 10*10*10 == 1000 values, and all
of those are less than or equal to n.


Another way to think of this is the slight less efficient but
probably easier to code
	LLL#### --> L | LL | ## | ##
	where L={A...Z} and #={0...9} 


You could also think of this as the also less efficient but also
probably easier to code

	CCCCCCC --> C | CC | CC | CC 
	where C={0...9A...Z}
since the range of CC is 36*36 values == 1296 which is less 
than or equal to n.


The ABSOLUTELY WRONG way to think of it would be
	LLL#### --> L | L | L | # | # | # | #