2519
Note that [x]>x−1 for any real number x. In particular, for an integer 1≤k≤10 we have ⌊kn⌋>kn−1, thus k⌊kn⌋>n−k. Since both sides are integers, we have k⌊kn⌋≥n−k+1, thus ⌊kn⌋≥kn−k+1. Since 0<k≤n implies kn−k+1>0, multiplying both sides of ⌊kn⌋≥kn−k+1 for k=1,2,…,10 yields
⌊1n⌋⌊2n⌋…⌊10n⌋≥1n⋅2n−1…10n−9=(10n).
Therefore the equation in the problem holds if and only if ⌊kn⌋=kn−k+1 for all integers 1≤k≤10.
If ⌊kn⌋=kn−k+1 holds, k divides n−k+1 because the right side is an integer. Conversely, if k divides n−k+1 then ⌊kn⌋=⌊kn−k+1⌋+kk−1=kn−k+1 holds. Therefore the equation ⌊kn⌋=kn−k+1 holds if and only if k divides n−k+1, that is, n+1 is a multiple of k.
Therefore, for an integer n≥10, the equation in the problem holds if and only if n+1 is a multiple of k for any integer 1≤k≤10, that is, n+1 is a common multiple of 1,2,…,10. Since the least common multiple of 1,2,…,10 is 2520, the smallest possible n is 2520−1=2519.