Candidate keys SQL

Question

hi am recently learning about SQL and keys.

i am wondering if there is n attributes to a relation table how many possible Candidate keys would there be?

Answer 1

Each subset of the attributes of the relations can be a candidate key. So the number is equal to the number of the subsets of a set of n elements, that is 2 ⁿ

Edited

The original answer was 2 ⁿ -1, but it significant also to have the empty (or niladic) key. A key of such kind implies that the relation has only one tuple. Thanks to @ErwinSmout for the clarification.