Leonhard Euler was born in 1707 in Switzerland. It is considered the most prolific mathematician of the history (in number of pages, as Paul Erdös published more articles). It is said that he could write a mathematical paper in the half-hour between the first and second call to dinner!
As soon as Euler finished a paper, he would put it on top of a growing pile that was awaiting for printer. Then, the printer would grab the articles from the top of the pile, so many times the dates of publication of Euler's papers ran counter to those of their composition. It was a confusion because some papers were based on previous ones, but the last ones were published before the first ones.
In the first picture you can see a titanium ring with the so-called Euler's identity, one of the most beautiful formulas of mathematics. It combines the important numbers e=2.71828..., π=3.14159..., i=√, 1 and 0.
The second picture is a stamp. There you can read another famous formula due to Euler: for any convex polyhedron, the number of vertices and faces together minus the number of edges equals 2.
Howard W. Eves, In mathematical circles, Prindle, Weber & Schmidt, Inc (1969)