GW is correct:
" A Hebrew spelling of Nero Caesar's name was Nrwn Qsr n, e,r, o, n; q, s, r. It has been documented by archaeological finds that a first century Hebrew spelling of Nero's name provides us with precisely the value of 666. Is it not remarkable that this most relevant emperor has a name that fits precisely the required sum? Is this sheer historical accident? But there is more.
Second, the textual variant. If you consult a Bible with marginal references you may notice something of interest regarding Revelation 13:18. Your reference may say something to the effect: "Some manuscripts read 616." The fact is that the number 666 in some ancient manuscripts of Scripture is actually changed to 616. But why? Was it changed accidentally, or on purpose?
The difference surely is no accident of sight made by an early copiest. The numbers 666 and 616 are not even similar in appearance in the original Greek--whether spelled out in words or written out as numerals. As textual scholars agree, it must be intentional.
A strong and most reasonable case may be made for the following probability. John, a Jew, used a Hebrew spelling of Nero's name in order to arrive at the figure 666. But when Revelation began circulating among those less acquainted with Hebrew, a well-meaning copiest who knew the meaning of 666 might have intended to make its deciphering easier by altering it to 616. It surely is no mere coincidence that 616 is the numerical value of "Nero Caesar," when spelled in Hebrew by transliterating it from its more widely familiar Latin spelling."