What is the number associated with the beast in Revelation?

Answer: 666

This calls for wisdom. Let the person who has insight calculate the number of the beast, for it is the number of a man. That number is 666.

“Here is a call for wisdom: Let the one who has insight calculate the number of the beast, for it is the number of a man, and that number is 666.”— Revelation 13:18 (BSB)