Leonhard Euler was born in Switzerland in 1707. He is considered the most prolific mathematician in history (based on the number of pages, while Paul Erdös, §5, 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 being printed. Then, the printer would grab the articles from the top and therefore many times the dates of the publication of Euler's papers ran counterwise to those of their composition. It was extremely misleading because some papers, which were based on previous ones, were actually published first.
In the first picture you can see Euler's identity, one of the most beautiful formulas in mathematics. It combines the important numbers e=2.71828..., π=3.14159..., i=√-1, 1 and 0.
The second picture is a stamp containing another famous formula by Euler: for any convex polyhedron, the number of vertices and faces together minus the number of edges equals 2.