Base 3

In base 3, each digit position represents a power of 3: the rightmost digit counts individual ones, the next counts groups of 3, the next counts groups of 3×3, and so on — the same place-value idea as base 10, just with 3 distinct digits instead of ten.

Base 61

Base 61 works the same way: the rightmost digit counts ones, the next counts groups of 61, the next counts groups of 61×61, and so on, using 61 distinct digits.