But that’s because for 3 the sequence is dividing by 3 not 2.

81, 27, 9, 3, 1, 1/3, 1/9, etc.

3^4, 3^3, 3^2, 3^1, 3^0, 3^(-1), 3^(-2), etc.

You’re not always halving, but the method is the same and it sometimes helps people understand the concept more easily.