Complete the series:4, 6, 11, 13, 18, ?

The pattern in the series is as follows:

• Start with 4, add 2 to get 6.
• Add 5 to 6 to get 11.
• Add 2 to 11 to get 13.
• Add 5 to 13 to get 18.

So, the pattern is to add 2, then 5, then 2, then 5, and so on.

Following this pattern, the next step would be to add 2 to the last number in the series (18).

So, 18 + 2 = 20.

Therefore, the next number in the series is 20.