  We prove that the algebra $\mI_n:=K\langle x_1, ..., x_n, \frac{\der}{\der
x_1},...,\frac{\der}{\der x_n}, \int_1, ..., \int_n\rangle $ of
integro-differential operators on a polynomial algebra is a prime, central,
catenary, self-dual, non-Noetherian algebra of classical Krull dimension $n$
and of Gelfand-Kirillov dimension $2n$. Its weak homological dimension is $n$,
and $n\leq \gldim (\mI_n)\leq 2n$. All the ideals of $\mI_n$ are found
explicitly, there are only finitely many of them ($\leq 2^{2^n}$), they commute
($\ga \gb = \gb\ga$) and are idempotent ideals ($\ga^2= \ga$). The number of
ideals of $\mI_n$ is equal to the {\em Dedekind number} $\gd_n$.
  An analogue of Hilbert's Syzygy Theorem is proved for $\mI_n$. The group of
units of the algebra $\mI_n$ is described (it is a huge group). A canonical
form is found for each integro-differential operators (by proving that the
algebra $\mI_n$ is a generalized Weyl algebra). All the mentioned results hold
for the Jacobian algebra $\mA_n$ (but $\GK (\mA_n) =3n$, note that
$\mI_n\subset \mA_n$). It is proved that the algebras $\mI_n$ and $\mA_n$ are
ideal equivalent.
