  For a positive integer t>1, an integer N is called t-free if the exponent of
any prime factor of N is less than t. Some works shown if N is t-free, then N
satisfies Robin's inequality, for t=5, 7, 11, 16. This article shows that the
condition of t-free can be resuced to "N cannot be divided by t-th power of 2".
I proved that if N cannot be divided by 17-th power of 2, then N satisfies
Robin's inequality.
