In the describe , it is say that "IP network contains a range of 2n IP addresses where 0 <= n <= 32. Network mask always has 32-n first bits set to one, and n last bits set to zero in its binary representation. "

Think of this :
Mask:
11111111.11111111.11111111.11110000
this is :
255.255.255.240

So, there is 16 IP adress can be use in the LAN.

So, I think it should be "IP network contains a range of '2^n' IP addresses where 0 <= n <= 32. Network mask always has 32-n first bits set to one, and n last bits set to zero in its binary representation. "