There's a planet out in space called Zargon ........

On this planet these are  numbers that are called ziffles
These numbers are ziffles $56, 105, 28, 63, 49$

These numbers are not ziffles: $100, 18, 65, 9, 76$

Only two of these numbers are ziffles: $16, 14, 57, 24, 70$

So what is special about the ziffles?