What common property unites all of the following numbers?

4, 9, 60, 101, 400, 450, 910, 1010

The set of numbers that share this common property is not limited to just these eight, but the list should provide enough information to solve it.

• Can we also assume that no other numbers below 1010 share this commonality? – breadbox Mar 13 '15 at 3:16
• @breadbox I didn't find any more below 1010 but there could have been some that I missed – Ben Mar 13 '15 at 3:50

 4=IV, 9=IX, 60=LX, 101=CI, 400=CD, 450=CDL, 910=CMX, 1010=MX