Foreign Mathematics

I got back on campus last weekend after a week stop in Istanbul. I have to say, the city is full of amazing things to see, but one thing in particular got my attention. When I first got hold of a Turkish 10 lira bill, I noticed a mathematical formula written in small on its reverse side. After an afternoon of wondering what this formula was all about, I got back to the hotel and 10 minutes later, I was reading the Wikipedia article on the Arf invariant.

I wish more countries had mathematics written on their currency.