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 points 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'.