I don't understand this premise: The reason for this is, I want to be able to read the array @a from every instance of $x. If I know @a always has $x coming at every 49th element, this is easy.

Could you explain more about your application?
I have no problem with some of the solutions in this thread to create this array with redundant information. But I am confused as to why this would be necessary or "easy"?