For letters: exclude I,L,O (ambiguous), so 23 unique values
- 000 000 000 (100M unique values)
- ABC 000 000 (one switch from letters to numbers) (~12G unique values)
- ABC DEF (148M)
- ABC DEF GHJ (~1800G unique values)
- ABCD EFGH (~78G unique values)
- other suggestions?
For letters: exclude I,L,O (ambiguous), so 23 unique values