  We present exact formulas for the form factors of local operators in the
repulsive Lieb-Liniger model at finite size. These are essential ingredients
for both numerical and analytical calculations. From the theory of Algebraic
Bethe Ansatz, it is known that the form factors of local operators satisfy a
particular type of recursive relations. We show that in some cases these
relations can be used directly to derive compact expressions in terms of the
determinant of a matrix whose dimension scales linearly with the system size.
Our main results are determinant formulas for the form factors of the operators
$(\Psi^{\dagger}(0))^2\Psi^2(0)$ and $\Psi^{R}(0)$, for arbitrary integer $R$,
where $\Psi$, $\Psi^{\dagger}$ are the usual field operators. From these
expressions, we also derive the infinite size limit of the form factors of
these local operators in the attractive regime.
