Six Hundred and Sixty-Six

Worked two ways: in Greek, χξϛ (chi 600 + xi 60 + stigma 6) = 666; in Hebrew, נרון קסר (Neron Qesar) = 50+200+6+50 + 100+60+200 = 666, and the shorter נרו קסר (Nero Qesar, without the final nun) = 616, which is the reading of one early manuscript.

Six hundred and sixty-six is the number of the beast, and the most defensible reading of it is also the oldest: the Hebrew letters of Nero Caesar's name give 666, and the shorter spelling gives 616 — precisely the variant found in Papyrus 115 — which is the strongest single argument that the number is a name and not a symbol. The tradition has also read it as Sorath, the spirit of the Sun in Agrippa's table, whose letters סורת sum to 666, and that reading is modern.