Suppose there are infinite points arranged as hexagonal lattice. The question is the one as the title. First we choose a point called $A$. Then when we count the $n$th nearest points to $A$, what number will I get. Actually I don't know whether this is a math problem or a more physics one.
I'm so sorry I misused the jargon hexagonal lattice. What I want to say is something arranged like graphene where points indeed make some hexagon rather than something points arranged like triangles. I'm so sorry I've made such a stupid mistake.