Used with permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA, http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps

Leonhard Euler (1707-1783), a Swiss mathematician, worked in number theory, differential geometry, calculus, differential equations, and is here commemorated with his polyhedron formula:

Number of vertices - number of edges + number of faces = 2

The Swiss stamp on the right shows a bewigged Euler and his formula relating the exponential and trigonometric functions in the complex plane.