What's the last number of infinity?
Since infinity goes on for infinity, there can't be a last number. And if there's no last number, then what's that last number?
Well, duh, zero, of course. Zero is the very last number. If there's no last number, then it's zero.
And here you were thinking there was no such thing as a last number. Ya learns somethin' new every day...
A math joke you can share at your next mathematics conference and everyone else will think you're the life of the party telling such funny jokes. Or, they'll groan at how bad it is. It could go either way.