A prefix reversal inverts the order of the first j genes, for some j > 1 and j ≤ n. For example, for the chromosome h5, 9, 6, 2, 1, 4, 7, 3, 8i we could get the result h6, 9, 5, 2, 1, 4, 7, 3, 8i or h1, 2, 6, 9, 5, 4, 7, 3, 8i from a prefix reversal. How many different prefix reversals are there for a 1000-gene chromosome?