  How many particles are necessary to make a quantum system many-body? To
answer this question, we take as reference for the many-body limit a quantum
system at half-filling and compare its properties with those of a system with
$N$ particles, gradually increasing $N$ from 1. We show that convergence for
the static properties of the system with few particles to the many-body limit
is fast. For $N \gsim 4$, the density of states is already very close to
Gaussian and signatures of many-body quantum chaos, such as level repulsion and
fully extended eigenstates, become evident. The dynamics, on the other hand,
depend on the initial state and time scale. In dilute systems, as the particles
move away from each other, the entropy growth changes in time from linear, as
typical for many-body systems, to logarithmic.
