[math-fun] "Was sind und was sollen die Zahlen?"

What does the title "Was sind und was sollen die Zahlen?" mean? I've seen it translated as "What are numbers and what should they be?". But I've also seen it translated as "What are numbers and what are they good for?", which is very different. (I only took one semester of German, but wouldn't "should be" be "sollen sein", rather than "sollen"?) Jim Propp