Revelation 14:9-11
And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,
Topicalbible.org—AKJV

Revelation 19:20
And the beast was taken, and with him the false prophet that worked miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
Topicalbible.org—AKJV

Revelation 13:18
Here is wisdom. Let him that has understanding count the number of the beast: for it is the number of a man; and his number is Six hundred three score and six.
Topicalbible.org—AKJV