  We consider two classes of non-Gaussian entangled states generated from the
product of number states with the action of the beamsplitter or the two-mode
squeezer. It is shown that, for many of these states, the covariance matrix is
compatible with the covariance matrix of separable Gaussian states and their
separability cannot be verified by the measurements of the first and second
moments of canonical variables. We identify a couple of continuous-variable
entanglement criteria with higher order moments to verify these non-Gaussian
entanglement.
