I need a spreadsheet with the following data: (in either format)

Format 1:

col 1 col 2 col3
a a a
a a b
a a c
a a d ...
z z z

format 2:

col1
aaa
aab
aac
aad ...
zzz


This spreadsheet will go on to list ALL the 17,000+ permutations.
Is there a formula or something that can either:
1. create the list automatically using the letters?
2. if i used numbers in format 1, is there a formula to convert the number
to it's equivalent letter ? 1=a, 2=b, c=3 etc.

Thanks for looking.

Ann