We have investigated the radicality and the vertical singlet triplet energy gap of [n]cyclacenes (cyclic polyacenes) as a function of the system size for n even, from 6 to 22. The calculations are performed using the complete active space self consistent field method and second-order n-electron valence perturbation theory. We present a systematic way for the selection of the active space in order to have a balanced description of the wave function as the size of the system increases. Moreover, we provide didactic insight into the failure of an approach based on a minimal active space. We find that the ground state is an open shell singlet and its multireference character increases progressively with n. The singlet triplet gap decreases as a function of the system size and approaches a finite positive value for the limit n -> infinity. Finally, an analysis based on the one-particle reduced density matrix suggests a polyradical character for the largest cyclacenes.