For example, Account IDs have prefix 001 and have 15 alphanumeric digits. What are the values for the first and last records that can be represented in this format (as we understand Salesforce IDs today)?
Looking at some account ids ordered by id asc in my dev org it seems the ordering sorts by 0-9 then a-z then A-Z.
0010a00001ACeQl
0010a00001CVCfp
0010a00001CVCfq
0010a00001CVCfr
001j0000003ZS1z
001j0000003ZS20
001j0000003ZS21
001j0000003ZS22
001j0000003ZS23
Therefore my guess is the range is between 001000000000000 and 001ZZZZZZZZZZZZ