There’s some numerical way that 666 means Nero.
In Hebrew lettering, his name would be Nrn Qsr (Neron Qaesar)
Hebrew doesn’t use a separate set of characters for numerals; each letter has a numerical value. The numerical values of “Nrn Qsr” add up to 666. But it’s disputed whether it would add up to 666 or 616, since “n” in a final position is a different letter than “n” elsewhere. Incredibly, many ancient copies of the New Testament say the number of the beast is 616!
666 for Reagan is simply the number of letters in each name of his: Ronald Wilson Reagan.
As a fun aside:
Ellen Burke White claimed that if you added up the letters in the Pope’s official title, you’d get 666, supposedly proving he was the anti-Christ. To get this, the alleged official title was “Vicar of the Son of God.” (VICarIVs fILeII DeI = VIC VI LII DI = 6+106+52+501 = 666, although translating the U to V is dubious) The problem is that the Pope is the vicar of Jesus in his human nature, so the Catholic title (only one of dozens) is “Vicar of the Son of Man.” Oddly however: eLLen goVLD VVhIte = LL VLD VVI = 100+555+11 = 666). Oops.