=2^n

No, no, no, no.

Can be explained by the knowledge of permutation and combination.

Suppose there are n balls, from which the balls are taken out, then all cases are 0, 1, 2, 3, ..., n, which is the left side of the equation. In all cases, each ball has two cases of being taken and not being taken, and n balls are * * * 2 n, which is the right side of the equation, so the equation holds.

It can also be concluded that the sum of odd terms is equal to the sum of even terms, which is equal to 2 (n- 1).