Dear Sergio Naldini,
Thanks for your concerns to our site!
Based on your itinerary, we would like to emphasize that you need visa to stay 17 days in Viet Nam
You can apply for 1 month visa minimum at this link: https://www.vietnam-evisa.org/apply-visa.html
There are two fees you are required to pay: The stamping fee (paid directly at Vietnam's airport) + our service fee for the approval letter (paid in advance). For instance, if you apply for the tourist visa with 1 month single entry, the service fee is 12USD/pax (paid online) and the stamping fee is 25USD/pax (paid in cash at the arrival airport).
Any help, please feel free to contact us at hotline :0909 343 525 or email at firstname.lastname@example.org
Helen Truong (Ms.)