A system of N two-dimensional weakly interacting bosons in a harmonic trap is considered. When the two-particle potential is a delta function Smith and Wilkin have analytically proved that the elementary symmetric polynomials of particle coordinates measured from the center of mass are exact eigenstates. In this study, we point out that their proof works equally well for an arbitrary two-particle potential which possesses the translational and rotational symmetries. We find that the interaction energy associated with the eigenstate with angular momentum L is equal to aN (N −1)/2+(b − a) N L/2, where a and b are the interaction energies of two bosons in the lowest-energy one-particle state with zero and one unit of angular momentum, respectively. Additionally, we study briefly the case of attractive quartic interactions. We prove rigorously that the lowest-energy state is the one in which all angular momentum is carried by the center of mass motion. 03.75.Fi,05.30.Jp,67.40.Db The study of Bose-Einstein condensation in trapped atomic gases has attracted a great deal of attention in the past few years [1][2][3][4]. One of the central issues has been the possibility of creating quantized vortices in these dilute atomic gases. Recently, vortex states in various systems have been experimentally observed [5,6]. Some theoretical investigations on quantized vortices and on rotating Bose condensates have also been carried out both in the Thomas-Fermi limit of strong interactions [7][8][9][10] and in the limit of weak interactions [11][12][13][14][15][16][17][18] between the atoms. For the weakly interacting bosons one is naturally led to study the model of N two-dimensional bosons in a harmonic trap with weak repulsive delta-function interactions [11]. One important theoretical problem here is to understand the properties of the system with a given total angular momentum L. Numerical studies have shown that when L > N the lowest-energy state is the one where an array of singly quantized vortices is formed [15,8]. However, due to the complexity of these states, very few analytic results are known. In the range 0 ≤ L ≤ N the structure of lowest-energy states turns out to be simpler. Numerical computations by Bertsch and Papenbrock [13] showed that the interaction energy of the lowest-energy states has a very simple form and decreases linearly with L (the only exception being that for L = 1). They also noted that the wave functions for the lowest-energy states are simply the elementary symmetric polynomials of complex coordinates relative to the center of mass. Very recently, this remarkable formula for interaction energy was derived analytically by Jackson and Kavoulakis [17]. Moreover, Smith and Wilkin [18] proved that these symmetric polynomials are indeed exact eigenstates (see Ref. [19] for an alternative proof). In this note, we point out that the analytic proof by Smith and Wilkin works not only for a delta-function potential but also for an arbitrary potential which possesses translational and rotational symmetri...