Revelation 13:16 (KJV)

And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.

And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.

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.