The Bible plainly says,

Revelation 13:16-18, “And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. 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.”

It also should be considered that the number 6 is the number of mankind. In Romans 6:6, the word “man” is the 6th word of the 6th verse of the 6th chapter of the 6th book of the New Testament. I don't get caught up into Biblical numerology that much, but it's preeminence throughout the Scriptures cannot be denied. God cleverly assembled the Bible in such a way that it is evident that the Lord loves numerology (the study of numbers).

God wouldn't have tossed out the challenge in Revelation 13:18 to compute the number of a man, who will be the Antichrist, unless it were possible to solve. At no point throughout history have Christians been able to discern Biblical prophecy as accurately as today, because we are blessed to literally be living in prophetic history (that is, prophecy is history written in advance). The New World Order is unfolding before our very eyes, being called for by name around the world by the leaders of nations, scholars, the Pope, scientists, educators and influential people from all walks of life.

We are witnessing prophetic history being fulfilled. I am confident that the challenge in Revelation 13:18 was put there by God for more than just our mere curiosity; but rather, as a lamp unto the feet of the saints who will be persecuted and many martyred during the Tribulation by the Antichrist. Remember, the Antichrist cannot be introduced to the world until the Rapture of the saints (2nd Thessalonians 2:7-8). So, in my humble thinking, I would think that the challenge of Revelation 13:18 will not be solvable until that time. I am grateful to God, and feel so blessed every time I read the Bible, to have such a clear view of Biblical prophecy.

The Old Testament prophets didn't understand what they wrote. The prophet Daniel even saw things from the End Times in visions, and desired to know what they meant, but God told him it wasn't meant for him. Daniel 12:8-9, “And I heard, but I understood not: then said I, O my Lord, what shall be the end of these things? And he said, Go thy way, Daniel: for the words are closed up and sealed till the time of the end.”

It is abundantly clear that we are now living in the End Times, during the time of the feet of iron and clay of Nebuchadnezzar's image. The Second Coming of Christ is represented in Nebuchadnezzar's dream by a STONE cut from a mountain without hands, which is Jesus Christ, who will smash the image (the kingdoms of this world), and establish His own Kingdom. Even so, come, Lord Jesus!