What comes next in the series? 7, 9, 18, 20, 40, 42, ___?

What comes next in the series? 7, 9, 18, 20, 40, 42, ___?

Explanation

 Add 2, then multiply by 2 →

7+2=9

9×2=18

18+2=20

20×2=40

40+2=42

42×2=84