Revelation 13:18 in the World English Bible
Here is wisdom. He who has understanding, let him calculate the number of the beast, for it is the number of a man. His number is six hundred sixty-six.
Context
17 And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
18 Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.