It has a time decaying value function. If the points accumulate rapidly upon submission, you can reach front page with as few as 5 up votes. This often happens for github repo submissions.
This sounds trivially gameable by voting rings.
It's not trivial to game over time. HN has been very successfully handling attempts at gaming for years. If it didn't, the site wouldn't function at all given its traffic, it would be overwhelmed with crap 24/7.