Revelation 13:18 in the King James Version
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.
Context
17 and that no one would be able to buy or to sell unless he has that mark, which is the name of the beast or the number of his name.
18 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.