I think you might want to rethink your post. Just using base36 numbers in bash to answer your post:

Code:

$ echo $((36#zzzzzzzzzzzz))
4738381338321616895

That is the largest 12 digit number in base36 - the gigantic number. It could easily take a desktop computer long time to count that high.
Every combination of base 36 number taken 12 at a time is much larger than the stupidly large number above.

I'm positive you need to tell us what you are trying to do, I've answered the question of how to print a decimal version base36 number, which is not what you asked. Mostly for completeness.

Code:

echo $((base#number))

Can you please tell us your requirement - example: generate 12 character passwords for linux.