<p>The behavior of Bose-Einstein condensates (BECs) near the Feshbach resonance is a challenging research area. We present a correlated many-body approach to calculate the atom number fluctuation at large scattering length when the trapped bosons interact via the realistic two-body van der Waals potential. Atom number fluctuation is the key property of strongly interacting finite-sized quantum systems. It is theoretically challenging when the particles become highly correlated. We observe that fluctuation is enhanced in the strongly interacting limit for the bosons trapped in a spherical potential. Introducing the anharmonicity, the atom number fluctuation and critical temperature of the condensate depend regourously on the number of particle. In the anharmonic trap, the trap geometry and interaction play an intricate role exhibiting maximal fluctuation at intermediate particle number.</p>