  High resolution numerical simulations of stationary inverse energy cascade in
two-dimensional turbulence are presented. Deviations from Gaussianity of
velocity differences statistics are quantitatively investigated. The level of
statistical convergence is pushed enough to permit reliable measurement of the
asymmetries in the probability distribution functions of longitudinal
increments and odd-order moments, which bring the signature of the inverse
energy flux. Their scaling laws do not present any measurable intermittency
correction. The seventh order skewness is found to increase by almost two
orders of magnitude with respect to the third, thus becoming of order unity.
