17/8 = 2.125 which has the decimal portion terminate or stop. This is not a repeating decimal. This is a terminating decimal.
The denominator 8 can be factored into 2*2*2. Since 2 is the only factor, this means that the decimal terminates. The same rule applies if 5 is present as a factor. If the denominator has other numbers (other than 2 or 5) as factors, then the decimal would repeat in some fashion.