They are different in several ways. The first number refers to the strength of the narcotic like pain reliever in them, the second to the amount of acetaminophen in them. The first contains half the narcotic type pain reliever and 60% of the acetaminophen of the second.
Oxycodone is also similar to but not the same as hydrocodone. Oxycodone is derived from thebaine and hydrocodone is derived from thebaine and codeine. Both effect the same general pathways in the brain and both can be addictive if abused.