Abstract. A number n > 1 is harmonic if σ(n) | nτ (n), where τ (n) and σ(n) are the number of positive divisors of n and their sum, respectively. It is known that there are no odd harmonic numbers up to 10 15 . We show here that, for any odd number n > 10 6 , τ (n) ≤ n 1/3 . It follows readily that if n is odd and harmonic, then n > p 3a/2 for any prime power divisor p a of n, and we have used this in showing that n > 10 18 . We subsequently showed that for any odd number n > 9 · 10 17 , τ (n) ≤ n