  The Chern numbers which correspond to quantized Hall conductance
$\sigma_{xy}$ were calculated for single- and bi-layer honeycomb lattices. The
quantization of $\sigma_{xy}$ occurs in entire energy range. Several large
jumps of Chern numbers appear at van-Hove singularities of energy bands without
magnetic fields. The plateauxof $\sigma_{xy}$ are discussed from semi-classical
quantization.
