Find the wrong number in the series.

7, 28, 63, 124, 215, 342, 511

28

On analyzing the following series, we get all the terms in this series is the subtraction of 1 from a cube of a number except 28 which is the addition of 1 in a cube of a number.

2³ - 1 = 7

3³+ 1 = 28

4³ - 1 = 63

5³ - 1 = 124

6³ - 1 = 215

7³ - 1 = 342

8³ - 1 = 511

So in place of 28, we need to correct it as 26 (3³ - 1).