You mean software patents? Because if you meant any patent, there are loads of good examples in pharmaceuticals (and chemicals more generally), and they are pretty much textbook examples of being "hard to discover, easy to reproduce from description".
Just off the top of my head: Viagra, Teflon, aspirin (the latter of which has long since expired or been seized as war reparations, depending on where you live).
Viagra was an ineffective drug that now gets sold based on a side-effect noted during testing for it's initial purpose. Maybe that's technically "hard to discover" but it's not really what initially leaps to mind when I hear that phrase.
If a drug that does what Viagra does wasn't hard to discover, why wasn't it invented before? And why would they bother pursuing the ED applications in the first place if someone could copy the formulation the moment it was substantiated?
Just off the top of my head: Viagra, Teflon, aspirin (the latter of which has long since expired or been seized as war reparations, depending on where you live).