In this paper, we find the greatest value p = log2/(log π − log 2) = 1.53 … and the least value q = 5/3 = 1.66 … such that the double inequality M p (a, b) 0 with a ≠ b. Here, M p (a, b) and T (a, b) are the p-th power and Seiffert means of two positive numbers a and b, respectively.