ISL 2000 A7

For a polynomial $P$ of degree 2000 with distinct real coefficients let $M(P)$ be the set of all polynomials that can be produced from $P$ by permutation of its coefficients. A polynomial $P$ will be called $n$ -independent if $P(n) = 0$ and we can get from any $Q \in M(P)$ a polynomial $Q_1$ such that $Q_1(n) = 0$ by interchanging at most one pair of coefficients of $Q.$ Find all integers $n$ for which $n$ -independent polynomials exist.