Even Factors

The number 10 has two even factors, 2 and 10; and two odd factors, 1 and 5. The number 12 has four even factors, 2, 4, 6, and 12; and two odd factors, 1 and 3. Find numbers whose factors are all even, except for the number 1. What do you notice about these numbers?

(Source: Adapted from Mathematics Teaching in the Middle School, Jan-Feb 1995)