5. Find the missing no?

Find the next term in the following series:
3, 5, 5, 19, 7, 41, 9, ?

Answer: 
71
Explanation:

The actual series is in this form

3, 3*2-1, 5, 5*4-1, 7, 7*6-1, 9, so the next term must be 9*8-1=71