Extended Strong's Greek Lexicon (Abbott-Smith based)
666
Usage: χξς ́ (on ς, see: Z), in T, Tr., Rec. for ἑξακόσιοι ἑξήκοντα ἕξ, six hundred and sixty-six (L, mg., R, mg., six hundred and sixteen), the mystical number of the Beast: Rev.13:18 (on the interpretation, see Swete, Ap., 172 f.).† (AS)