  Hankel tensors are generalizations of Hankel matrices. This article studies
the relations among various ranks of Hankel tensors. We give an algorithm that
can compute the Vandermonde ranks and decompositions for all Hankel tensors.
For a generic $n$-dimensional Hankel tensor of even order or order three, we
prove that the the cp rank, symmetric rank, border rank, symmetric border rank,
and Vandermonde rank all coincide with each other. In particular, this implies
that the Comon's conjecture is true for generic Hankel tensors when the order
is even or three. Some open questions are also posed.
