What is the subnet mask for 31?

How many IP addresses are in a 31?

address?

Is 31 a good choice to use when creating an IP address pool? This will be a class with 12 students. I am unsure of the IP assignment I need to be using to determine all students IP addresses. What would be a good pool size for all students?
Thanks. Jodi.e. Here's a very brief description of why your IP Address must be changed in certain cases. (The examples used are based on a pool of 100 computers.)

You would normally distribute IP addresses on the basis of the following needs: If you have two computers in each class (a total of about 50 computers) the chances are reasonably good that they will both require an IP address. You do not want a client in your class to have multiple IP addresses from their computer as this will cause IP conflicts and performance problems. 100 computers in a class gives about 50 individual IP addresses for distributing to the clients. 2 computers per class will allow one computer to share one IP address. 3 computers per class will allow one computer to have two IP addresses. 4 computers per class will allow one computer to have three IP addresses. 5 computers per class will allow one computer to have four IP addresses. 6 computers per class will allow one computer to have five IP addresses. 7 computers per class will allow one computer to have six IP addresses. 8 computers per class will allow one computer to have seven IP addresses. 9 computers per class will allow one computer to have eight IP addresses. 10 computers per class will allow one computer to have nine IP addresses. So, just from the example above and ignoring the fact that IP addresses are not used statically, the conclusion is that 31 computers per class will allow one computer to have 31 IP addresses (unless you get up to 33 or 34 computers per class as this would give a computer one extra IP address). However, what you cannot do is share the existing pool of IP addresses between these classes (ie one class can use another class's pool and then not have an additional IP address on each computers). So it would make more sense to split the existing pool of 100 addresses into two equally sized pools of 100 computers, giving 50 computers per class, and use one set for this class, and the other set for another class.