What comes next in the series 4, 6, 9, 13........................?

What comes next in the series 4, 6, 9, 13........................?

Explanation

Finding the pattern:

6−4=2

9−6=3

13−9=4

The differences between consecutive numbers are +2, +3, +4.

Following this pattern, the next difference should be +5.


So, 

13+5=18.