17so that no one can buy or sell unless he has the mark, that is, the name of the beast or the number of its name.
As you read through this paragraph, it is clear that the beast mentioned in Revelation 13:17 (and Revelation 13:18) is the first beast, described in Revelation 13:1–10.
17 so that no one can buy or sell unless he has the mark, that is, the name of the beast or the number of its name.