Hexakosioihexekontahexaphobia is the fear of which number?

Hexakosioihexekontahexaphobia is the fear of the number 666. The reason for this is that 666 is the "Number of the Beast", as written in the New Testament book Revelation. The "Beast" is generally thought to be the devil / antichrist and when the antichrist does appear, all his followers will have the mark of the beast somewhere on their body.

This word itself is derived from ancient Greek roots; hexakósioi, "six hundred", hexékonta, "sixty", héx, "six", and phóbos, "fear"; literally meaning "fear of six hundred sixty-six".

Some people try very hard to avoid the number 666. When US President Ronald Reagan and his wife Nancy moved to a new home in Bel-Air the address was 666 St. Cloud Street. As soon as they were able they had it changed to 668.

There was a highway in New Mexico USA that was designated US 666. There seemed to be quite a few accidents on that road, and so it was changed to US 491. This was done several years ago and so far there are no statistics that indicate any change.

There are scholars that believe that the number was mistranslated, and that the real number of the beast is 616. But the number 666 has been in common use for centuries, and so continues to be a symbol of the devil/antichrist.