Are 'the prisoner's card numbers '666' a reference to a certain aspect of the plot? Does it repeat along the series?

In the series "The prisoner" season 1 ep 1 (I only saw it for now), the protagonist, number '6', receives his cards to access services on the island. The scene is the following:

At this point you can see three of his cards in a folder, forming '666'

Is that a reference to some aspect of the plot? Does it repeat along the series?

A central element of the plot seems to be the island authorities trying to figure why number 6 quit his (apparently excellent) job, an act which apparently doesn't fit his profile.

In Iron Maiden's song "The prisoner", inspired in the series, which is part of the album "The number of the beast", there are references to doing what one pleases(as an animal or 'natures beast' does):

"Going all the way, I'm nature's beast. Do what I want, I do as I please."

"Don't care where the past was, I know where I'm going..."

This last one seems to suggest the lyrical subject regrets a decision in the past, since he had to state he doesn't care what happened but appears be saying he doesn't want 'guidance'(maybe 'forced guidance') because 'he (now) knows where he is going'.

User Draakhond (thanks) reminded of the following:

Bible - Revelation 13: 16-18

It also forced all people, great and small, rich and poor, free and slave, to receive a mark on their right hands or on their foreheads, so that they could not buy or sell unless they had the mark, which is the name of the beast or the number of its name.This calls for wisdom. Let the person who has insight calculate the number of the beast, for it is the number of a man.[e] That number is 666

Among the cards were his identity card, his health care card and his credit card.

Here, apparently 'the beast' has a different meaning from that alluded by Iron Maiden's song (even though Iron Maiden's Album itself evokes the biblical context). The beast is the powerful apocalyptic entity who attempted against god and his saints, apparently "conquered" the world and required people to comply with its rules in order to be allowed to participate in the economy. The beast here seems to be "that which constraints" rather than "that which is constrained".

I don't know what the book of Revelation really means, so any insights here are also appreciated.