1723

This number is a prime.

Proving the Riemann Hypothesis is equivalent to showing floor(H(n)+e^{H(n))*log(H(n)}) ≥ σ(n), where H(n) = 1 + 1/2 + 1/3 + ... + 1/n, and σ(n) is the sum of the divisors of n. For example, when n = 17, the two sides differ by 23. [Caldwell]