From the comment:

> then you should use one of the many alternative structures available. Some of them were explicitly designed to store integers in an efficient manner.

From the article:

> But if you do want to save memory you could consider using an SplFixedArray for large, static arrays. ... It basically does the same thing, but if you run it, you’ll notice that it uses “only” 5600640 bytes. That’s 56 bytes per element ...

EDIT: formatting.