Base 7

In base 7, each digit position represents a power of 7: the rightmost digit counts individual ones, the next counts groups of 7, the next counts groups of 7×7, and so on — the same place-value idea as base 10, just with 7 distinct digits instead of ten.

Base 5

Base 5 works the same way: the rightmost digit counts ones, the next counts groups of 5, the next counts groups of 5×5, and so on, using 5 distinct digits.