John invites believers having the wisdom to “interpret scripture with scripture” solve the riddle of 666 meaning. That is confirmed by the parallel to “Here is wisdom” ωδε ἡ σοφία ἐστίν in Revelation 17:9, “here the mind which has wisdom” ὧδε ὁ νοῦς ὁ ἔχων σοφίαν. Just as the “mind which has wisdom” solves the riddle of the “seven heads” being both mountains and kings using Old Testament Scripture, so do believers solve John’s riddle.
"Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six (Rev. 13:18 KJV)
John gives three clues: 1) “Counting” reveals 666 IS the number of the Antichrist Beast; 2)“Counting” that results in 666 reveals it is the “number OF a man”. 3)The number 666 is the Biblical allusion identifying the Old Testament scriptures necessary to solve the riddle.
The children of Adonikam, six hundred sixty and six. (Ezr. 2:13) KJV
The children of Adonikam, six hundred threescore and seven. (Neh. 7:18) KJV
John’s riddle is based on BOTH 666 and 667 being correct. The different counts arise because both Father and son are named Adonikam:
Ezra counts Firstborn Adonikam’s children, therefore 666 is “the number OF a man” because generating 666 children brought the number into existence. Nehemiah’s count of Father Adonikam’s children includes his firstborn Adonikam, so his children total 667.
Hence, 666 is the Janus pivot that reveals the "number of the Beast as we “count” (5585 ψηφίζω psephizo), and his name “Adonikam”.
Counting backward from Adonikam’s father, we deduce 666 number is OF the Beast because when we count as with pebbles from Father Adonikam (667-1=666) “his (the Beast’s) number is 666”. Counting forward reveals the number itself comes into being because of firstborn Adonikam, a count of his children is 666. So it is "the “number OF a man”
Whether we count forward or backward the Name Adonikam appears.
Therefore, name of the Beast is Adonikam.