No, seriously! How is zero a number? I understand it’s on the number line and mathematics doesn’t quite operate without it. However, mathematics doesn’t quite operate with other things that aren’t numbers, like a plus sign. A plus sign is not a number yet math doesn’t work without it.
In fact, the number line does not work without a plus sign (you cannot advance from 1 to 2 without “adding” 1). So what differentiates zero as an Integer, or number as opposed to a tool of mathematics?