Revelation 13

16 And he causes all people, the small and the great, and the rich and the poor, and the free and the slave, that they give them a mark on their right hand or on their forehead, 17 and that no one was able to buy or to sell except the one who had the mark—the name of the beast or the number of his name. 18 Here is wisdom: the one who has understanding, let him calculate the number of the beast, for it is man’s number,*Or "it is the number of a man" and his number is six hundred sixty-six.*A few significant manuscripts read "six hundred sixteen"