18 Here is the wisdom. The one having understanding, let him count the number of the beast, for it is a man’s number, and its number is six hundred sixty-six.
Revelation 13:18 Cross References - BLB
Mark 13:14
14 And when you see the abomination of the desolation, standing where it should not (the one reading, let him understand), then those in Judea, let them flee to the mountains;
Romans 3:5
5 But if our unrighteousness shows God’s righteousness, what shall we say? God, inflicting the wrath, is unrighteous? I speak according to man.
Revelation 1:3
3 Blessed is the one reading, and those hearing the words of the prophecy, and keeping the things having been written in it; for the time is near.
Revelation 15:2
2 And I saw something like a sea of glass mingled with fire, and those conquering over the beast, and over its image, and over the number of its name, standing upon the sea of glass, having harps of God.
Revelation 17:9
9 Here is the mind having wisdom: The seven heads are seven mountains, where the woman sits on them;
Revelation 21:17
17 And he measured its wall, one hundred forty-four cubits, the measure of man, that is of the angel.