What are the next two terms in the pattern ,3,6,5,10,9,18,17?

Answer 1

Not even the very sophisticated Wolfram couldn't find a pattern

www.wolframalpha.com/input/?i=pattern+%7B3%2C6%2C5%2C10%2C9%2C18%2C17%7D

Answer 2

double, subtract 1, double, subtract 1, ...
3,6,5,10,9,18,17,34,33,66,65, ...