17hats will only connect directly to a Google calendar, but you can sync a Google calendar to Outlook for a two way sync. This method is not supported by 17hats, but the following article will provide the guidelines for connecting Google Calendar and an Outlook Calendar.
Log into your Google calendar and click on the small arrow to the right of the calendar you want to sync to Outlook and click on 'Calendar Settings'
Under calendar settings scroll down to 'Private Address', then click on the 'ICAL' icon, a box pops up with a link, copy the link.
Go to outlook online and click on 'Add Calendar', then click on 'From Internet':
A dialog box pops up, add the link you copied from Google, and provide a name for this calendar, then click on 'Save'.
All events from the Google calendar you attached will now show on your Outlook Calendar.
For instructions on connecting via your Desktop based outlook please look at the following Microsoft Article: