11, 22, 13, 26, 15, 30, 17...What's next?

Okay, so far I have tried to find the rule but I could not get the pattern.

11, 22 } +11

22, 13 } -9

13, 26 } +13

26, 15 } -11

15, 30 } +15

30, 17 } -30

WTH is the pattern!!!???

I have been stuck on this question for 30 minutes. I need help finding the pattern. Thanks!