Revelation 13

16 And it makes everyone — small and great, rich and poor, free and slave — to receive a mark on his right hand or on his forehead,  * 13:16 Rv 14:1,9,11; 16:2; 19:20; 20:417 so that no one can buy or sell unless he has the mark: the beast’s name or the number of its name.

18 This calls for wisdom:  * 13:18 Or Here is wisdom,* 13:18 Rv 17:9 Let the one who has understanding calculate  * 13:18 Or count, or figure out the number of the beast, because it is the number of a person. Its number is 666.  * 13:18 Other Gk mss read 616