On the conformal properties of topological terms in even dimensions

Conformal properties of the topological gravitational terms in $D=2$, $D=4$ and $D=6$ are discussed. It is shown that in the last two cases the integrands of these terms, when being settled into the dimension $D-1$ and multiplied by a scalar, become conformal invariant. Furthermore we present a simple covariant derivation of the Paneitz operator in $D=4$ and formulate two general conjectures concerning the conformal properties of topological structures in even dimensions.