What is the maximum auto generated id in Google App Engine datastore?

Question

What is the maximum auto generated id in Google App Engine datastore?

Why this question?

I would like to show a more user-friendy id to my customer in a format like ####-####-#### using the alphabet:

 0123456789ABCDEFGHIJKLMNPQRSTUVWXYZ

the character O has been removed to avoid confusion with the digit 0.

I need to know how many groups of ### are needed to represent all the ids.

Answer 1

2^53 (the integer portion of a 64-bit float)