17 Republicans?

https://edition.cnn.com/2021/01/13/politics/senate-impeachment-process-next-steps/index.html

How many votes are required to convict Trump?

Great question! Conviction requires 2/3 of those present. If all 100 senators are present, that's 67 senators. Assuming those two Georgians are seated, that means there are 50 senators from each party and 17 Republicans would be required.

However! Pay close attention to the rules, which require 2/3 of those present. If those two Democrats from Georgia are not yet seated, it might require 66 senators. If some number of Republicans didn't want to vote against Trump but also didn't want to vote to convict, they could skip the vote and change the ratio. That kind of thing has been known to happen, although not during impeachment proceedings.