This brings back memories, and I am disappointed that I was so late even seeing this. In the math course I took my senior year in high school the instructor as fun extra credit would give us four digits (0-9) and challenge us to see how many natural numbers we could form starting at 0 and up [0,1,2, . . .] using each of those four digits once and only once. We were allowed to make use of not only +, -, *, /; but also factorials (treating 0!=1) and powers. Try it some time and you will be surprised at how far one may get.