Particle column density versus time after self-gravity is turned on at t₀ = 52T_orb = 326.726Ω^-1 in the simulation SI64_e0.3_NS. An overdense sheet forms by the streaming instability and breaks up in a number of gravitationally bound clumps. We indicate the number of clumps and their masses, in units of the mass of the dwarf planet Ceres, in the lower left part of the plots. Between 3 and 4 clumps condense out independently of how collisions are treated, with masses slightly smaller than Ceres. Clump merging, likely driven by the artificially large sizes of the planetesimals, reduces the number of clumps with time in all cases. Note that the initial condition for all four simulations is taken from SI64_e0.3_NS.