The address 172.16.208.16/20 which subnet

If I'm not mistaken, the /20 notation means that the 20 highest order bits are 1, and the other bits are 0. In binary that would be

11111111.11111111.11110000.0000

Or

255.255.240.0

If my math is correct, that should give you 4,096 addresses from 172.16.208.0 to 172.16.223.255.