Base 2

In base 2, each digit position represents a power of 2: the rightmost digit counts individual ones, the next counts groups of 2, the next counts groups of 2×2, and so on — the same place-value idea as base 10, just with 2 distinct digits instead of ten.

Base 7

Base 7 works the same way: the rightmost digit counts ones, the next counts groups of 7, the next counts groups of 7×7, and so on, using 7 distinct digits.