In the paper here, there is a plot of $R_{xx}$ as a function of magnetic field $B_{⊥}$ and carrier density, $n$.
The filling factor jumps by 4 between adjacent lines.
The set of lines where $R_{xx}= 0$ seems to be defined as 'Landau fan.'
$R_{xx}=0$ when the fermi energy is between bands, as shown in this image below (from wikipedia). 
I was also able to find in the paper here that for graphene with 4 fold degeneracy, $\nu = \pm 4(|n|+1/2)$.
I would like to know the general relation between the filling factor and the landau level (I wasn't able to find a clear equation showing the relation between the two. For instance, the equation I found for four fold degenerate graphene, on top of the factor of 4, it has an offset of $1/2$.
