Greek Nerón kaisar → Hebrew/Aramaic nrwn qsr "Emperor Nero" = 666 (Majority Text)
Latin Neró caesar → Hebrew/Aramaic nrw qsr "Emperor Nero" = 616 (P 115 , Irenaeus, Adversus Haereses 5.30.1)
The value of nun was 50, which accounts for the difference between 616 and 666. The many various clues given in ch. 13 and 17 also make clear that the author was talking about an emperor of Rome, particularly Nero (who at the time was widely believed to return). In Jewish-Christian tradition the figure of Nero was fused with that of the antichrist, as can be seen in the Ascension of Isaiah and the Sibylline Oracles.